Isoprene

• Formula: C₅H₈
• Molecular weight: 68.1170
• IUPAC Standard InChI: InChI=1S/C5H8/c1-4-5(2)3/h4H,1-2H2,3H3 Copy

  
• IUPAC Standard InChIKey: RRHGJUQNOFWUDK-UHFFFAOYSA-N Copy
• CAS Registry Number: 78-79-5
• Chemical structure:
  This structure is also available as a 2d Mol file or as a computed 3d SD file
  The 3d structure may be viewed using Java or Javascript.
• Other names: 1,3-Butadiene, 2-methyl-; β-Methylbivinyl; Isopentadiene; 2-Methyl-1,3-butadiene; 2-Methylbutadiene; CH2=C(CH3)CH=CH2; 2-Methylbuta-1,3-diene; 3-Methyl-1,3-butadiene; NSC 9237
• Permanent link for this species. Use this link for bookmarking this species for future reference.
• Information on this page:
  • Gas phase ion energetics data
  • References
  • Notes
• Other data available:
  • Gas phase thermochemistry data
  • Condensed phase thermochemistry data
  • Phase change data
  • Reaction thermochemistry data
  • Henry's Law data
  • Ion clustering data
  • IR Spectrum
  • Mass spectrum (electron ionization)
  • UV/Visible spectrum
  • Gas Chromatography
• Data at other public NIST sites:
  • Microwave spectra (on physics lab web site)
  • Gas Phase Kinetics Database
• Options:
  • Switch to calorie-based units

Data at NIST subscription sites:

• NIST / TRC Web Thermo Tables, professional edition (thermophysical and thermochemical data)

NIST subscription sites provide data under the NIST Standard Reference Data Program, but require an annual fee to access. The purpose of the fee is to recover costs associated with the development of data collections included in such sites. Your institution may already be a subscriber. Follow the links above to find out more about the data in these sites and their terms of usage.

Gas phase ion energetics data

Go To: Top, References, Notes

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Data evaluated as indicated in comments:
HL - Edward P. Hunter and Sharon G. Lias
L - Sharon G. Lias

Data compiled as indicated in comments:
B - John E. Bartmess
LL - Sharon G. Lias and Joel F. Liebman
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard

View reactions leading to C₅H₈⁺ (ion structure unspecified)

Ionization energy determinations

Appearance energy determinations

De-protonation reactions

C₅H₇^- +  =

By formula: C₅H₇^- + H⁺ = C₅H₈

References

Go To: Top, Gas phase ion energetics data, Notes

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Hunter and Lias, 1998
Hunter, E.P.; Lias, S.G., Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update, J. Phys. Chem. Ref. Data, 1998, 27, 3, 413-656, https://doi.org/10.1063/1.556018 . [all data]

Bieri, Burger, et al., 1977
Bieri, G.; Burger, F.; Heilbronner, E.; Maier, J.P., Valence ionization enrgies of hydrocarbons, Helv. Chim. Acta, 1977, 60, 2213. [all data]

Lossing and Traeger, 1975
Lossing, F.P.; Traeger, J.C., Stabilization in cyclopentadienyl, cyclopentenyl, and cyclopentyl cations, J. Am. Chem. Soc., 1975, 97, 1579. [all data]

Puttemans and Delvaux, 1973
Puttemans, J.-P.; Delvaux, J.C., Ionisation et fragmentation d'isomeres C₅H₈ sous impact electronique. Spiropentane - methylenecyclobutane - isoprene, Ing. Chim. Brussell, 1973, 55(267-8), 7. [all data]

Beez, Bieri, et al., 1973
Beez, M.; Bieri, G.; Bock, H.; Heilbronner, E., The ionization potentials of butadiene, hexatriene, andtheir methyl derivatives: evidence for through space interaction between double bond π-orbitals and non-bonded pseudo-π orbitals of methyl groups?, Helv. Chim. Acta, 1973, 56, 1028. [all data]

Watanabe, Nakayama, et al., 1962
Watanabe, K.; Nakayama, T.; Mottl, J., Ionization potentials of some molecules, J. Quant. Spectry. Radiative Transfer, 1962, 2, 369. [all data]

Price and Walsh, 1940
Price, W.C.; Walsh, A.D., The absorption spectra of conjugated dienes in the vacuum ultra-violet (1), Proc. Roy. Soc. (London), 1940, A174, 220. [all data]

Werstiuk, Clark, et al., 1990
Werstiuk, N.H.; Clark, K.B.; Leigh, W.J., Conformational analysis and structure elucidation of 2,3-dimethyl and 2,4-dimethyl-2,4-hexadienes by AM1 and He(I) ultraviolet photoelectron spectroscopy, Can. J. Chem., 1990, 68, 2078. [all data]

Masclet, Mouvier, et al., 1981
Masclet, P.; Mouvier, G.; Bocquet, J.F., Effets electroniques et effets steriques dus a la substitution alcoyle dans les dienes conjugues, J. Chim. Phys., 1981, 78, 99. [all data]

Worley, Webb, et al., 1979
Worley, S.D.; Webb, T.R.; Gibson, D.H.; Ong, T.-S., On the electronic structures of cyclobutadiene trimethylenemethane, J. Organomet. Chem., 1979, 168, 16. [all data]

Sustmann and Schubert, 1972
Sustmann, R.; Schubert, R., Photoelektronenspektroskopische bestimmung von substituenten-effekten. I. Subtituierte butadiene, Tetrahedron Lett., 1972, 27, 2739. [all data]

Lossing and Holmes, 1984
Lossing, F.P.; Holmes, J.L., Stabilization energy and ion size in carbocations in the gas phase, J. Am. Chem. Soc., 1984, 106, 6917. [all data]

Harrison, Haynes, et al., 1965
Harrison, A.G.; Haynes, P.; McLean, S.; Meyer, F., The mass spectra of methyl-substituted cyclopentadienes, J. Am. Chem. Soc., 1965, 87, 5099. [all data]

Holmes, 1974
Holmes, J.L., The mass spectra of isomeric hydrocarbons - II: The C₅H₈ isomers, spiropentane, cyclopentene, 1,3-pentadiene and isoprene; the mechanisms and energetics of their fragmentations, Org. Mass Spectrom., 1974, 8, 247. [all data]

Bartmess and McIver Jr., 1979
Bartmess, J.E.; McIver Jr., The Gas Phase Acidity Scale in Gas Phase Ion Chemistry, Gas Phase Ion Chemistry, V. 2, M.T. Bowers, Ed., Academic Press, NY, 1979, Ch. 11, Elsevier, 1979. [all data]

Notes

Go To: Top, Gas phase ion energetics data, References

• Symbols used in this document:
  

  AE	Appearance energy
  IE (evaluated)	Recommended ionization energy
  ΔrG°	Free energy of reaction at standard conditions
  ΔrH°	Enthalpy of reaction at standard conditions

• Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
• The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data contained therein have been selected on the basis of sound scientific judgment. However, NIST makes no warranties to that effect, and NIST shall not be liable for any damage that may result from errors or omissions in the Database.
• Customer support for NIST Standard Reference Data products.