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C5H8

C₅H₈ is the molecular formula for a diverse group of isomeric hydrocarbons composed of five carbon atoms and eight hydrogen atoms, primarily featuring unsaturation in the form of double bonds, triple bonds, or rings.^[1] These compounds have a calculated degree of unsaturation of 2, which accounts for structures such as dienes (two double bonds), alkynes (one triple bond), or combinations of rings and double bonds.^[2] There are at least 26 constitutional isomers of C₅H₈, spanning several structural classes including three alkynes (e.g., pent-1-yne and pent-2-yne), multiple dienes (e.g., penta-1,3-diene and penta-1,4-diene), eight cycloalkenes (e.g., cyclopentene and methylcyclobutene), and bicyclic saturated compounds (e.g., housane).^[1] Some isomers also exhibit stereoisomerism, such as E/Z geometrical isomers in dienes or R/S optical isomers in chiral structures.^[1] Among the most significant isomers is isoprene (2-methylbuta-1,3-diene), a volatile, colorless liquid that serves as the monomeric unit of natural rubber and a fundamental building block in the biosynthesis of terpenoids and isoprenoids.^[3] Another key compound is cyclopentene, a cyclic monoalkene that appears as a colorless liquid with a petrol-like odor and finds applications in the synthesis of pharmaceuticals, polymers, and other organic materials. These isomers collectively play roles in industrial chemistry, natural product synthesis, and atmospheric processes, with many being commercially available or derived from petroleum sources.^[4]

Molecular characteristics

Formula and basic properties

C₅H₈ is the molecular formula denoting hydrocarbons composed of five carbon atoms and eight hydrogen atoms. The molar mass of these compounds is 68.12 g/mol.^[3] These hydrocarbons are unsaturated, featuring two degrees of unsaturation when compared to the saturated alkane C₅H₁₂ (pentane), which accounts for the presence of double bonds, triple bonds, or rings in their structures.^[5] At room temperature, most C₅H₈ isomers appear as colorless liquids.^[3]^[6] Boiling points for common isomers typically range from 25–45 °C, as exemplified by isoprene at 34 °C and cyclopentene at 44 °C.^[3]^[7] These compounds are generally insoluble in water due to their nonpolar nature but exhibit good solubility in organic solvents such as ethanol and ether.^[8]^[9] Properties among isomers vary slightly owing to structural differences.

Degree of unsaturation

The degree of unsaturation (DU), also known as the index of hydrogen deficiency, is calculated using the formula DU = (2C + 2 - H - X + N)/2, where C is the number of carbon atoms, H is the number of hydrogen atoms, X is the number of halogen atoms, and N is the number of nitrogen atoms.^[10] For the molecular formula C₅H₈, with C = 5, H = 8, X = 0, and N = 0, the calculation yields DU = (2×5 + 2 - 8)/2 = 2.^[10] This value indicates the total number of rings and/or pi bonds in the molecule relative to its saturated hydrocarbon counterpart.^[11] A DU of 2 for C₅H₈ signifies two degrees of unsaturation, which can manifest as two double bonds, one triple bond, one double bond combined with one ring, or two rings.^[12] These structural features arise because each double bond or ring accounts for one degree, while a triple bond contributes two degrees by effectively incorporating two pi bonds.^[10] Such unsaturations introduce pi electrons that delocalize and influence molecular geometry, often leading to planar or strained configurations depending on the arrangement.^[13] Compared to the fully saturated alkane C₅H₁₂ (DU = 0), molecules with DU = 2 exhibit heightened reactivity due to the presence of pi bonds or rings, which facilitate addition reactions and lower activation energies for transformations.^[14] This unsaturation also impacts stability, as pi systems can be less thermodynamically stable than sigma-bonded alkanes, evidenced by higher heats of combustion.^[13] In spectroscopy, these features produce characteristic signals, such as C=C stretching absorptions in the IR spectrum around 1620–1680 cm⁻¹.^[15] For context, related formulas like C₅H₁₀ (DU = 1) represent mono-unsaturated systems, while C₅H₆ (DU = 3) indicates higher unsaturation levels with even greater reactivity potential.^[10]

Constitutional isomers

Acyclic alkynes

The acyclic alkynes with the molecular formula C5H8 consist of three constitutional isomers: pent-1-yne (CH₃CH₂CH₂C≡CH), pent-2-yne (CH₃CH₂C≡CCH₃), and 3-methylbut-1-yne ((CH₃)₂CHC≡CH). These compounds feature a single carbon-carbon triple bond in an open-chain hydrocarbon skeleton, satisfying the degree of unsaturation equivalent to two double bonds or one triple bond.^[16]^[17] Pent-1-yne and 3-methylbut-1-yne are terminal alkynes, characterized by a linear or branched alkyl chain attached to a -C≡CH group, where the triple bond is at the end of the chain. In contrast, pent-2-yne is an internal alkyne with the triple bond positioned between two alkyl groups (ethyl and methyl), resulting in a more symmetrical linear structure. None of these isomers exhibit stereoisomerism, as the linear geometry of the triple bond precludes cis-trans or optical isomers.^[16] Terminal alkynes like pent-1-yne and 3-methylbut-1-yne possess an acidic hydrogen atom on the terminal carbon, with a pKa of approximately 25, allowing deprotonation by strong bases to form acetylide anions for nucleophilic reactions. Internal alkynes such as pent-2-yne lack this acidity due to the absence of a terminal hydrogen. Internal alkynes are generally more thermodynamically stable than terminal ones, owing to greater hyperconjugation and reduced strain from alkyl substitution on the triple bond.^[18]^[19]^[20] Physical properties reflect their structural differences; for example, pent-1-yne has a boiling point of 40 °C, pent-2-yne boils at 56–57 °C due to increased molecular symmetry and van der Waals interactions, and 3-methylbut-1-yne has a lower boiling point of 29.5 °C from its branched structure reducing surface area.^[21]^[22]

Acyclic dienes and allenes

The acyclic dienes and allenes of C₅H₈ represent six constitutional isomers characterized by two double bonds, either non-cumulated (dienes) or cumulated (allenes). These structures satisfy the formula's degree of unsaturation without rings or triple bonds, featuring linear or branched carbon chains. The dienes include both conjugated systems, where double bonds are adjacent and their π orbitals overlap, and isolated systems, where the double bonds are separated by a saturated carbon. In contrast, allenes possess cumulative double bonds (C=C=C), resulting in orthogonal π bonds that impart distinct geometric and stereochemical properties.^[23] Among the dienes, penta-1,4-diene (H₂C=CHCH₂CH=CH₂) exemplifies an isolated diene with double bonds separated by one methylene group, leading to independent reactivity of each alkene unit; its boiling point is 26 °C.^[24] Penta-1,3-diene (CH₃CH=CHCH=CH₂) is a conjugated diene that exists as (E)- and (Z)-stereoisomers due to restricted rotation around the internal double bond, with a boiling point of 42 °C.^[25] The branched isomer, 2-methylbuta-1,3-diene or isoprene (H₂C=C(CH₃)CH=CH₂), also features conjugation but with a methyl substituent on one of the sp² carbons, enhancing its volatility (boiling point 34 °C) and influencing electronic distribution in the π system.^[26]^[27] The allenes include penta-1,2-diene (CH₂=C=CHCH₂CH₃), a terminal allene with one unsubstituted methylene group, boiling at 44.9 °C.^[28] Penta-2,3-diene (CH₃CH=C=CHCH₃) is an internal allene that demonstrates axial chirality, existing as (R)- and (S)-enantiomers because the perpendicular π bonds prevent free rotation and the identical methyl substituents on each end create non-superimposable mirror images.^[29]^[23] Its boiling point is approximately 48 °C.^[30] Finally, 3-methylbuta-1,2-diene ((CH₃)₂C=C=CH₂, also known as 3-methyl-1,2-butadiene) is a branched terminal allene with a boiling point of 41 °C. In allenes, the central sp-hybridized carbon forms two perpendicular π bonds using orthogonal p orbitals, which underlies their chirality when substituents differ and contributes to their reactivity, such as in cycloadditions orthogonal to typical alkenes.^[23]^[31]

Monocyclic alkenes

Monocyclic alkenes with the formula C5H8 feature a single carbocyclic ring and one carbon-carbon double bond, corresponding to two degrees of unsaturation. These isomers are distinguished by ring size and the position of the double bond, either endocyclic or exocyclic, along with alkyl substituents. Eight constitutional isomers exist in this class, with some exhibiting stereoisomerism due to chiral centers. The five-membered ring representative is cyclopentene, characterized by an endocyclic double bond between carbons 1 and 2 in a nearly planar ring. This compound is a stable, colorless liquid with a boiling point of 44 °C and a density of 0.77 g/cm³ at 25 °C. Four-membered ring isomers include methylenecyclobutane, which has an exocyclic double bond (=CH₂) attached to the cyclobutane ring, 1-methylcyclobutene with an endocyclic double bond and a methyl group on one of the sp²-hybridized carbons, and 3-methylcyclobutene with the methyl substituent on an sp³ carbon adjacent to the double bond. Methylenecyclobutane boils at 42 °C, indicating higher volatility compared to cyclopentene due to its lower molecular symmetry and reduced intermolecular forces. 3-Methylcyclobutene possesses a chiral center at carbon 3, resulting in (R) and (S) enantiomers. Cyclobutene derivatives experience notable angle strain, with C-C-C bond angles near 90° deviating from the tetrahedral ideal of 109.5°, which contributes to their relative instability and enhanced reactivity in ring-opening processes.^[32] Three-membered ring isomers comprise the ethylcyclopropenes—1-ethylcyclopropene (ethyl group on an sp² carbon) and 3-ethylcyclopropene (ethyl on the sp³ carbon)—as well as the dimethylcyclopropenes, including 1,2-dimethylcyclopropene (methyls on the double bond carbons) and 1,3-dimethylcyclopropene (methyls on one sp² and the sp³ carbon). The 1,3-dimethylcyclopropene features a chiral center at position 3, yielding (R) and (S) optical isomers. Cyclopropene structures exhibit extreme ring strain from 60° bond angles and partial π-bond character in the strained ring, rendering them highly reactive toward addition reactions and thermal isomerization.^[33]

Bicyclic and polycyclic structures

Bicyclic and polycyclic hydrocarbons with the formula C5H8 possess two degrees of unsaturation entirely from ring systems, resulting in highly strained structures due to compressed bond angles and torsional effects in small rings. These compounds are characterized by cyclopropane-like units, where angle strain exceeds 60°, significantly higher than in larger cycloalkanes, leading to reduced stability and increased reactivity. The total ring strain in such systems can reach 265 kJ/mol, as seen in representative examples, making them challenging to synthesize and handle.^[34] A prominent example is spiropentane, or spiro[2.2]pentane, consisting of two cyclopropane rings sharing a single spiro carbon atom at the quaternary center. This structure exhibits exceptional strain from the orthogonal arrangement of the rings and the forced 90° dihedral angles at the spiro junction, contributing to its torsional strain in addition to angle strain. Spiropentane has a boiling point of approximately 39 °C and demonstrates kinetic stability under ambient conditions despite its high strain energy, though it can undergo ring-opening reactions under catalytic or thermal stress.^[35]^[36] Another key isomer is housane, or bicyclo[2.1.0]pentane, featuring a fused cyclobutane and cyclopropane ring with a bridge of zero carbons between positions 1 and 4. The [2.1.0] bridging notation highlights the highly strained central cyclopropane bond, which is elongated compared to standard cyclopropanes due to transannular interactions. Housane is a volatile liquid with a boiling point around 45 °C and low thermal stability, decomposing above 60 °C to form less strained isomers; its strain arises primarily from the folded geometry and bond angle deviations exceeding those in isolated small rings.^[37] Bicyclo[1.1.1]pentane represents a bridged system with three one-carbon bridges connecting two bridgehead carbons, forming a highly symmetric yet strained cage-like structure. The bridgehead carbons are connected solely by the three methylene bridges, resulting in a bridgehead-to-bridgehead distance of approximately 1.87 Å due to severe repulsion and strain. The overall strain is around 100-110 kJ/mol, driven by angle compression and torsional effects in the methylene bridges. This isomer exhibits remarkable rigidity and has been studied for its potential in medicinal chemistry as a bioisostere, though its synthesis requires multi-step processes to mitigate instability.^[38] Other strained bicyclic forms include variants such as ethylidenecyclopropane fusions and dimethylcyclopropane-bridged systems, though ethylidenecyclopropane incorporates exocyclic unsaturation and is reclassified elsewhere. These additional structures, like certain [1.1.1] or [2.1.0] derivatives with asymmetric bridges, contribute to a total of at least nine constitutional isomers, several of which display optical activity due to chiral bridgehead configurations or non-superimposable mirror images. High strain in these smaller bicycles generally results in low stability, with some prone to explosive decomposition under mechanical shock or high pressure.^[39]

Functional groups and reactivity

Alkene and alkyne functionalities

Alkenes in C5H8 isomers, such as cyclopentene, exhibit characteristic reactivity dominated by electrophilic addition reactions due to the electron-rich π-bond of the C=C double bond. For instance, addition of HBr to cyclopentene proceeds via a carbocation intermediate, yielding bromocyclopentane as the product following Markovnikov's rule, where the hydrogen adds to the carbon with more hydrogens.^[40]^[41] Another key reaction is catalytic hydrogenation, which saturates the double bond to form the corresponding C5H10 alkane; the general equation is:

\text{R-CH=CH-R'} + \text{H}_2 \xrightarrow{\text{catalyst (e.g., Pd)}} \text{R-CH}_2\text{-CH}_2\text{-R'}

This process is exothermic and typically requires a metal catalyst like palladium or platinum under mild conditions.^[42]^[43] Alkyne functionalities in C5H8 isomers display distinct reactivity, particularly for terminal alkynes like pent-1-yne, which possess acidic C-H bonds (pKa ≈ 25) due to the sp-hybridized carbon. These can be deprotonated by strong bases such as sodium amide (NaNH₂) to form acetylide anions, which are useful nucleophiles in synthesis; internal alkynes like pent-2-yne lack this terminal hydrogen and are far less acidic. A representative reaction is the formation of sodium acetylides:

\text{RC≡CH} + \text{Na} \rightarrow \text{RC≡CNa} + \frac{1}{2} \text{H}_2

This deprotonation highlights the enhanced reactivity of terminal alkynes compared to alkenes, primarily in acid-base and nucleophilic contexts, stemming from the greater s-character of the C-H bond.^[44]^[45]^[46] Spectroscopically, alkene and alkyne groups in these isomers can be identified via infrared (IR) absorption. The C=C stretch appears as a medium-intensity band at 1640–1680 cm⁻¹, while the C≡C stretch occurs at 2100–2260 cm⁻¹, often weak or absent for symmetrical internal alkynes due to low change in dipole moment. These ranges aid in distinguishing the unsaturation types in C5H8 compounds.^[47]^[48]^[49]

Diene conjugation and allene properties

Conjugated dienes among the C5H8 isomers, such as 1,3-pentadiene and isoprene (2-methylbuta-1,3-diene), display distinctive reactivity arising from the overlap of pi orbitals across the two adjacent double bonds, enabling delocalization of electrons in the allylic system. This conjugation stabilizes reactive intermediates like allylic carbocations, facilitating pathways beyond simple alkene additions.^[50] In electrophilic additions, such as with HBr, the reaction involves protonation to form a resonance-stabilized allylic carbocation, resulting in competing 1,2- and 1,4-addition products. For 1,3-pentadiene, the 1,2-addition product is 3-bromopent-1-ene, formed by direct capture at the adjacent carbon, while the 1,4-addition yields 1-bromopent-2-ene via attack at the resonated position. The 1,2-product predominates under kinetic control at low temperatures (e.g., -80°C), whereas the more stable 1,4-product is favored under thermodynamic control at higher temperatures (e.g., 40°C).^[51]^[52] This behavior is illustrated in the following scheme for 1,3-pentadiene:

\ce{CH2=CH-CH=CH-CH3 + HBr ->[kinetic, 1,2-addition] CH2=CH-CHBr-CH2-CH3 \ (3-bromopent-1-ene)}

\ce{->[thermodynamic, 1,4-addition] BrCH2-CH=CH-CH2-CH3 \ (1-bromopent-2-ene)}

Isoprene exhibits analogous addition patterns, with the methyl group influencing regioselectivity toward the 1,4-product in thermodynamic conditions.^[53] Conjugated dienes also undergo pericyclic reactions, notably the Diels-Alder cycloaddition, where they serve as the 4π-component partnering with electron-poor dienophiles in a [4+2] fashion to yield cyclohexenes. Isoprene, as a diene, reacts efficiently with dienophiles like acrolein or ethylene, producing para-substituted cyclohexenes due to its electron-donating methyl group directing the orientation (ortho-para rule analog). This reactivity has been extensively studied, with rate enhancements observed under Lewis acid catalysis.^[54]^[55] Allenes in C5H8 isomers, exemplified by penta-2,3-diene (CH3-CH=C=CH-CH3), possess cumulated double bonds where the central carbon is sp-hybridized, resulting in two orthogonal π systems perpendicular to each other. This geometry prevents free rotation and confers axial chirality when the terminal substituents are dissimilar, as the two methyl groups in penta-2,3-diene lie in mutually perpendicular planes, rendering the molecule chiral without a stereogenic center and existing as stable enantiomers.^[56]^[57] The orthogonal π bonds in allenes promote asymmetric reactivity in additions, where incoming reagents interact selectively with one π system, often leading to stereoselective products. For instance, electrophilic additions to penta-2,3-diene proceed via vinyl carbocation intermediates, favoring attack on the less substituted double bond and yielding allylic halides with potential for enantiofacial selectivity. Nucleophilic additions, such as with organocopper reagents, similarly exploit the perpendicular bonds for regioselective allylation.^[56]^[58] Infrared spectroscopy distinguishes these systems: conjugated dienes show C=C stretching bands shifted to lower wavenumbers around 1600 cm⁻¹ due to weakened bonds from delocalization, often appearing as two closely spaced peaks from coupled vibrations. Allenes display characteristic asymmetric C=C=C stretching at approximately 1950 cm⁻¹ (strong) and symmetric stretching near 1070 cm⁻¹ (weak), arising from the unique cumulated structure./13%3A_Structure_Determination_-_Mass_Spectrometry_and_Infrared_Spectroscopy/13.06%3A_IR-Absorption_Frequencies_of_Organic_Functional_Groups)^[59]

Occurrence and applications

Natural occurrence

Isoprene, or 2-methylbuta-1,3-diene, serves as the predominant C₅H₈ isomer in natural environments, functioning as a key volatile organic compound released by terrestrial vegetation. Plants such as oak and poplar trees emit isoprene primarily through leaf stomata, with global biogenic emissions averaging approximately 456 Tg C yr^-1 over 2013–2020, and present-day estimates ranging from 434–510 Tg C yr^-1 as of 2025, representing about 2% of photosynthetically fixed carbon.^[60] These emissions peak in tropical and temperate forests, where environmental stressors like heat and drought enhance production via the methylerythritol phosphate pathway in chloroplasts.^[61] Cyclopentene appears in trace quantities within petroleum and natural gas deposits, comprising less than 0.1 wt% of certain hydrocarbon source materials derived from ancient organic matter.^[62] Similarly, 1,3-pentadiene occurs in select essential oils, such as those extracted from Pittosporum tobira leaves, where it contributes to the volatile profile alongside other hydrocarbons.^[63] It also forms during the thermal decomposition of biomass, as observed in pyrolysis products from lignocellulosic materials like tobacco waste and coffee shells.^[64] Other C₅H₈ dienes, including precursors to larger terpenoids, are integral to plant-derived natural rubber and resin biosynthesis, originating from metabolic pathways in species like Hevea brasiliensis. Collectively, these isomers, particularly isoprene, influence atmospheric processes; isoprene's photooxidation in the troposphere generates peroxy radicals that promote ozone formation in the presence of nitrogen oxides, while also yielding secondary organic aerosols that affect climate and air quality.^[65]

Industrial production and uses

Isoprene, the most commercially significant C5H8 isomer, is primarily produced through the recovery of C5 fractions from ethylene cracking processes, where it appears as a byproduct in refinery streams derived from petroleum naphtha pyrolysis.^[3]^[66] Alternatively, it can be synthesized via thermal cracking of hydrocarbons such as isobutene or through oxidative processes involving propylene and ethylene derivatives.^[67] Global production capacity for isoprene was approximately 1.7 million metric tons per year in 2022, with actual output around 850 thousand metric tons in 2023; as of 2025, expansions such as Sinopec's 50% increase have raised capacity further, while bio-isoprene production is emerging with a market value of about USD 174 million in 2024.^[68]^[69]^[70]^[71] Approximately 95% of isoprene is polymerized into synthetic polyisoprene rubber, mimicking natural rubber for tires, footwear, and automotive components due to its elasticity and resilience.^[72] The remainder serves as a precursor for resins, adhesives, and fine chemicals.^[3] Cyclopentene, another key isomer, is industrially obtained via steam cracking of naphtha or partial hydrogenation of cyclopentadiene derived from dicyclopentadiene thermal cracking.^[62] It finds application as an intermediate in the synthesis of adiponitrile, a critical precursor for hexamethylenediamine used in nylon-6,6 production, enabling the formation of durable fibers and engineering plastics.^[73] 1,3-Pentadiene, commonly known as piperylene, is produced by thermal dehydrogenation of n-pentane or separation from C5 refinery streams during naphtha processing.^[74] Annual global production is estimated in the tens of thousands of metric tons, primarily for use as a comonomer in synthetic resins and adhesives. Terminal alkynes such as pent-1-yne are synthesized via dehydrohalogenation routes and employed in pharmaceutical intermediates for drug synthesis, leveraging their reactivity in coupling reactions.^[75] Allene isomers of C5H8 undergo coordination polymerization to form specialty polymers with unique optical and mechanical properties for niche applications in coatings and electronics.^[76] Conjugated dienes like isoprene and piperylene contribute to pressure-sensitive adhesives, enhancing tackiness and cohesion in tapes and labels through copolymerization with styrene.^[77]

References

[1]
26 selected constitutional isomers of molecular formula C5H8, E/Z ...
There are at least 26 constitutional isomers of molecular formula C5H8, including alkynes, dienes, and cyclic (alicyclic) saturated and unsaturated compounds.
[2]
Degree of Unsaturation
Its degree of unsaturation is 1, which is determined by subtracting H2n from H2n+2 and dividing the difference by 2.
[3]
Isoprene | C5H8 | CID 6557 - PubChem - NIH
Isoprene is a hemiterpene with the formula CH2=C(CH3)CH=CH2; the monomer of natural rubber and a common structure motif to the isoprenoids.<|control11|><|separator|>
[4]
C5H8 isomers - Molport
These 15 commercially available compounds have molecular formula C5H8.
[5]
7.2 Calculating the Degree of Unsaturation – Organic Chemistry
For example, the formula C5H8O is equivalent to the hydrocarbon formula C5H8 and thus corresponds to two degrees of unsaturation.
[6]
Cyclopentene | C5H8 | CID 8882 - PubChem - NIH
Cyclopentene appears as a colorless liquid. Less dense than water and insoluble in water. Flash point below 0 °F. Vapors heavier than air.
[7]
Cyclopentene, 95+% - Fisher Scientific
PubChem CID, 8882. ChEBI, CHEBI:49155. IUPAC Name, cyclopentene. SMILES, C1CC=CC1 ... Boiling Point, 44.0°C. Infrared Spectrum, Authentic. Packaging, Glass bottle.<|separator|>
[8]
Cyclopentene CAS#: 142-29-0 - ChemicalBook
Highly flammable. Insoluble in water. ... Cyclopentene may react vigorously with strong oxidizing agents. May react exothermically with reducing agents to release ...
[9]
Cyclopentene - Shandong Baiding Chemical Co., LTD
Appearance: Colorless liquid. Solubility: insoluble in water, soluble in ethanol, ether, benzene and other organic solvents.
[10]
[PDF] 5.12 Lecture 10 10
Degrees of unsaturation = number of rings and/or multiple bonds. 1 degree of unsaturation = 1 ring or 1 double bond. 2 degrees of unsaturation = 2 double ...
[11]
Illustrated Glossary of Organic Chemistry - Double bond equivalent ...
DBE = UN = PBoR = C - (H/2) + (N/2) +1, where: C = number of carbon atoms, H = number of hydrogen and halogen atoms, and N = number of nitrogen atoms. One DBE ...
[12]
chapter 1. introduction to organic chemistry
Determine the degrees of unsaturation based on the molecular formula. DU = 1 + 6 − ½ (10) = 2. Two degrees of unsaturation means that there is some ...
[13]
[PDF] 1 Chapter 6. Alkenes: Structure and Stability Degrees of ...
Multiple bonds are considered equivalent to the same number of single bonded atoms. The greater release of heat, the less stable the reactant. Table 6.2 (pg ...Missing: compounds | Show results with:compounds
[14]
CH105: Chapter 8 - Alkenes, Alkynes and Aromatic Compounds
Unsaturated hydrocarbons—hydrocarbons with double or triple bonds—on the other hand, are quite reactive. In fact, they serve as building blocks for many ...
[15]
IR Absorption Table
Alkenyl C-H Stretch Alkenyl C=C Stretch, 3100 - 3010 (m) 1680 - 1620 (v), Absorption peaks above 3000 cm-1 are frequently diagnostic of unsaturation ; Alkynyl ...
[16]
The number of possible alkynes with molecular formulae, - C 5 H 8
So the structures we obtained are – pent-1-yne, pent-2-yne and 3-methyl but-1-yne i.e. in total of three structures. So the correct option for the question is ...
[17]
Draw and name all the possible pentyne isomers, C_5H_8.
The possible isomers of C 5 H 8 are drawn below: Pent-1-yne, the first isomers, has five carbon atoms arranged in a straight chain with a triple bond.
[18]
10.8: Acidity of Terminal Alkynes - Chemistry LibreTexts
Feb 13, 2019 · Acidity of Terminal Alkynes and Acetylilde Ion Formation · ethanol (pKa = 16) · acetic acid (pKa = 4.72) · acetylene (pKa = 25).
[19]
Ch 9 : Acidity of Terminal Alkynes - University of Calgary
Terminal alkynes are unusual for simple hydrocarbons in that they can be deprotonated (pKa = 26) using an appropriate base (typically NaNH2, pKa = 36) to ...
[20]
4.9: Properties and Bonding in the Alkynes - Chemistry LibreTexts
Jul 5, 2021 · With the result of the production of butane, the stability of internal versus terminal alkynes has significant relative stability due to ...Bonding and Hybridization · Contributors · Alkynes are High In Energy
[21]
https://www.sigmaaldrich.com/US/en/product/aldrich/271357
[22]
3-METHYL-1-BUTYNE | 598-23-2 - ChemicalBook
Sep 25, 2025 · 3-METHYL-1-BUTYNE Properties. Melting point, -89.7°C. Boiling point, 29,5°C. Density, 0.666 g/mL at 25 °C (lit.) RTECS, PF9060500. Flash point ...
[23]
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Basic_Principles_of_Organic_Chemistry_(Roberts_and_Caserio)/13%3A_Polyfunctional_Compounds_Alkadienes_and_Approaches_to_Organic_Synthesis/13.05%3A_Cumulated_Alkadienes
[24]
1,4-Pentadiene
### Summary for 1,4-Pentadiene
[25]
1,3-Pentadiene
### Summary for 1,3-Pentadiene
[26]
https://pubchem.ncbi.nlm.nih.gov/compound/6557
[27]
Isoprene
### Summary for Isoprene (ID: 78-79-5)
[28]
https://webbook.nist.gov/cgi/cbook.cgi?ID=C591957
[29]
1,3-Dimethylallene | C5H8 | CID 136378 - PubChem - NIH
1,3-Dimethylallene, also known as 2,3-Pentadiene, has the molecular formula C5H8 and a molecular weight of 68.12 g/mol.
[30]
591-96-8(2,3-PENTADIENE) Product Description - ChemicalBook
2,3-PENTADIENE Property ; Melting point: -125.65°C ; Boiling point: 48.2°C ; Density, 0.6900 ; refractive index, 1.4251 ...
[31]
Synthetic Applications of Cyclopropene and Cyclopropenone ...
Jun 10, 2020 · Cyclopropenes possess high ring strain energy1 and treated as extremely reactive units with a wide spectrum of remarkable activities.
[32]
Analysis of several high-resolution infrared bands of spiropentane ...
As the simplest bicyclic ring compound, the structure and physical properties of spiropentane are of special interest. The ring strain in spiropentane (265 ...
[33]
https://aces.onlinelibrary.wiley.com/doi/10.1002/ajoc.202000193
[34]
Spiropentane as a tensile spring | Journal of the American Chemical ...
Combined Electron-Diffraction and Spectroscopic Determination of the Structure of Spiropentane, C5H8. ... Fluorination effect on the structural properties ...
[35]
Housane - an overview | ScienceDirect Topics
In housane 94′, the folding angle is 88.46(2)°, as expected for a housane. Upon irradiation or at temperatures above 60 °C, the housane isomerises to a formal ...Missing: boiling | Show results with:boiling
[36]
Molecular structure of bicyclo[1.1.1]pentane - ACS Publications
Mar 1, 1970 · Origin of strain in bicyclo[1.1.1]pentane. Tetrahedron Letters 1985 ... C5H8, Bicyclo[1.1.1]pentane. , 1-1. https://doi.org/10.1007 ...
[37]
[PDF] Thermochemistry of Organic and Organohalogen Compoundsf
For example, the strain energy of one three- membered ring in spiropentane is 132.8 kJ mol"1, which exceeds by -17 kJ mol"1 the strain energy of cyclopropane.
[38]
7.8: Electrophilic Addition Reactions of Alkenes - Chemistry LibreTexts
Apr 3, 2024 · Both the alkene and the hydrogen halide are reactants in the first step of the mechanism, this electrophilic addition is a second order reaction ...
[39]
Chapter 6 Notes: Alkene Reactions
alkenes react with hydrogen halides to form alkyl halides. Addition of HX to Alkenes. cyclohexene + HBr --> bromocyclohexane; 1-methylcyclohexene + HBr --> 1- ...<|separator|>
[40]
Catalytic Hydrogenation of Alkenes - Chemistry LibreTexts
Jan 22, 2023 · In a hydrogenation reaction, two hydrogen atoms are added across the double bond of an alkene, resulting in a saturated alkane.
[41]
Hydrogenation of Alkenes to give Alkanes - Master Organic Chemistry
In the presence of a metal catalyst such as palladium, hydrogen will add to alkenes to give alkanes.
[42]
Acetylides from Alkynes, and The Substitution Reactions of Acetylides
May 1, 2013 · Terminal alkynes have unusually acidic C–H bonds (pKa 25). Treatment with a strong base such as sodium amide (NaNH2) gives an acetylide, the ...
[43]
9.7: Alkyne Acidity - Formation of Acetylide Anions
Mar 18, 2024 · Consequently, acetylide anions can be readily formed by deprotonation of a terminal alkynes with a sufficiently strong base. The amide anion ...
[44]
9.3: Reactions of Alkynes - Addition of HX and X₂
Mar 24, 2024 · The reactions of alkynes are even more exothermic than the additions to alkenes, and yet the rate of addition to alkynes is slower by a factor ...
[45]
11.5: Infrared Spectra of Some Common Functional Groups
May 30, 2020 · In alkenes compounds, each band in the spectrum can be assigned: C=C stretch from 1680-1640 cm -1; =C–H stretch from 3100-3000 cm -1 ...
[46]
IR Spectroscopy Tutorial: Alkenes
The stretching vibration of the C=C bond usually gives rise to a moderate band in the region 1680-1640 cm-1. Stretching vibrations of the –C=C–H bond are of ...
[47]
IR: alkynes
The –C≡C– stretch appears as a weak band from 2260-2100 cm-1. This can be an important diagnostic tool because very few organic compounds show an absorption in ...
[48]
https://orgchemboulder.com/Spectroscopy/irtutor/alkenesir.shtml
[49]
[PDF] Chapter 7 - UMSL
The major product obtained from addition of HBr to 1,3-pentadiene is 4-bromo-2-pentene (A ... 1,2-addition product and the 1,4-addition product. Page 6 ...
[50]
HBr Addition to Conjugated Pi Systems - YouTube
Feb 1, 2015 · This video describes the addition of HX (in this case it's HBr) to 1,3-pentadiene. Kinetic vs. thermodynamic control and 1,2- vs. 1,4- ...
[51]
Reactions of Dienes: 1,2 and 1,4 Addition - Master Organic Chemistry
Mar 22, 2017 · Kinetic and thermodynamic control in addition of HBr to dienes can give 1,2- and 1,4- products. How do we explain this? Examples, mechanism, &
[52]
The Diels-Alder Reaction of Isoprene with Styrene and 2 ...
Vinylazaarenes as dienophiles in Lewis acid-promoted Diels–Alder reactions. ... Structural orientation in the diene condensations of isoprene with unsymmetrical ...
[53]
How Lewis Acids Catalyze Diels–Alder Reactions - PMC - NIH
The Lewis acid(LA)‐catalyzed Diels–Alder reaction between isoprene and methyl acrylate was investigated quantum chemically using a combined density functional ...
[54]
Chemical Reactivity - MSU chemistry
Since the π-bonds of allenes are orthogonal, the planes defined by the end carbon substituents are also orthogonal. As shown in the following diagram, the ...Missing: perpendicular | Show results with:perpendicular
[55]
R and S Configuration of Allenes - Chemistry Steps
Chirality of Allenes In order for the allene to be chiral, each terminal carbon must be connected to two different atoms/groups. For example, allene (A) is ...
[56]
Mechanistic Aspects and Synthetic Applications of Radical Additions ...
Because the k2/k1 of penta-2,3-diene (1,3-dimethylallene) was higher than that of, it was surmised that penta-2,3-diene is more reactive than propadiene toward ...
[57]
Infrared absorption intensities of allene - American Institute of Physics
Discrepancy is only remarkable for the parameter P:u. (antisymmetric CH stretching), the value of which is much smaller in allene than in ethylene. This fact ...
[58]
Evolution of isoprene emission capacity in plants - ScienceDirect.com
Light-dependent de novo volatile isoprene emission by terrestrial plants (approximately 2% of carbon fixed during photosynthesis) contributes as much as 0.5 Pg ...Opinion · Highlights · References (75)
[59]
Isoprene Emission from Plants: Why and How - PMC - NIH
Isoprene emission is the predominant biogenic source of hydrocarbon in the atmosphere, roughly equal to global emission of methane from all sources.Why Isoprene Emissions... · Thermotolerance · Mep Pathway Regulation
[60]
Cyclopentene - an overview | ScienceDirect Topics
Cyclopentene is an aliphatic hydrocarbon with a five-membered carbon ring and one double bond, present in source material at less than 0.1 wt%.Missing: petroleum | Show results with:petroleum
[61]
Larvicidal effects of the major essential oil of Pittosporum tobira ...
tobira essential oil (PTEO) was 0.1%, and GC-MS analysis identified its major constituents as undecane (31.11%), 4-methyl-1,3-pentadiene (11.34%), (1,3 ...
[62]
A Comparative Analysis of Waste Biomass Pyrolysis in Py-GC-MS ...
Apr 19, 2023 · The percentage area of alkenes (1,3-pentadiene) was discovered in TW (confirmed in other studies of this type [35]) and CS samples, but alkenes ...
[63]
[PDF] Secondary Organic Aerosol Formation from Isoprene Photooxidation
Recent work has shown that the atmospheric oxidation of isoprene (2-methyl-1,3-butadiene, C5H8) leads to the formation of secondary organic aerosol (SOA).
[64]
Overview of isoprene monomer and polyisoprene production ...
Commercial production involves separation of isoprene monomer from C5 ethylene by-product streams through a series of fractionation and extraction distillation ...
[65]
Isoprene price index - businessanalytiq
Isoprene can be synthesized industrially from petroleum-derived feedstocks. The most common method is the thermal cracking of hydrocarbons such as isobutene or ...
[66]
Isoprene Production Capacity, Demand-Supply, Pricing and Market ...
The global isoprene production capacity was estimated to be approximately 1,700 kilotons in 2022. Asia-Pacific and Central & Eastern Europe collectively ...
[67]
GLOBAL ISOPRENE MARKET 2023-2030 - Triton Market Research
The Global Isoprene Market is growing at a CAGR of 7.65% expected to reach $4859.79 million, during the forecast period 2023-2030.
[68]
Isoprene Monomer Market - Share, Size and Industry Analysis
Isoprene monomer is widely used in the production of synthetic rubber called as polyisoprene. ... use industry segment over the forecast period. Key ...<|separator|>
[69]
Enhancing selectivity and efficiency in the electrochemical synthesis ...
Nov 15, 2018 · Adiponitrile is a large scale chemical intermediate used in the production of Nylon 6,6. It is primarily produced via two methods: the ...
[70]
1,3-Pentadiene | C5H8 | CID 62204 - PubChem
1,3-pentadiene appears as a clear colorless liquid with an acrid odor. A dangerous fire risk. Vapors are irritating to the eyes and respiratory system.
[71]
[PDF] 1,3-PENTADIENE CAS N°:504-60-9
At least 10 to 50 million pounds (4536-22680 t) per year of 1,3-pentadiene are produced.
[72]
1-Pentyne | C5H8 | CID 12309 - PubChem - NIH
Molecular Formula. C5H8. Synonyms. 1-PENTYNE; pent-1-yne; 627-19-0; Propylacetylene; MFCD00009469. View More... Molecular Weight. 68.12 g/mol. Computed by ...
[73]
Polymerization of Allenes by Using an Iron(II) β‐Diketiminate Pre ...
Jun 18, 2021 · There are many reported studies that use allenes as coupling partners in annulation and addition reactions, as building blocks in organic ...
[74]
The Chemical Properties and Industrial Production of Isoprene (78 ...
Oct 12, 2025 · In this scenario, Isoprene is separated from the mixed C5 hydrocarbon stream through selective extraction and distillation processes.
[75]
Piperylene - Wikipedia
Piperylene or 1,3-pentadiene is an organic compound with the formula CH 3−CH=CH−CH=CH 2. It is a volatile, flammable hydrocarbon. It is one of the five ...