unsaturated hydrocarbons

(noun)

A molecule where some of the carbons are connected to fewer than four neighboring atoms. Usually the molecule contains double or triple bonds.

Related Terms

Examples of unsaturated hydrocarbons in the following topics:

  • Alkenes & Alkynes

    • Alkenes and alkynes are hydrocarbons which respectively have carbon-carbon double bond and carbon-carbon triple bond functional groups.
    • The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups:
    • As noted earlier in the Analysis of Molecular Formulas section, the molecular formula of a hydrocarbon provides information about the possible structural types it may represent.

  • Substitution Reactions of Benzene and Other Aromatic Compounds

    • The remarkable stability of the unsaturated hydrocarbon benzene has been discussed in an earlier section.

  • Introduction to Hydrocarbons

    • Hydrocarbons are the simplest class of organic compounds, consisting solely of hydrogen and carbon.
    • Hydrocarbons are the simplest class of organic compounds and are composed solely of hydrogen and carbon.
    • This class can be further divided into two groups: aliphatic hydrocarbons and aromatic hydrocarbons.
    • Alkenes and alkynes are known as unsaturated hydrocarbons because some of the carbons are connected to fewer than four neighboring atoms.
    • The study of hydrocarbons is particularly important to the fields of chemical and petroleum engineering, as a variety of hydrocarbons can be found in crude oil.

  • Alkanes

    • Alkanes are relatively unreactive hydrocarbons that contain no double or triple bonds in their carbon skeletons.
    • Alkanes, also called paraffins, are a class of hydrocarbons that are fully saturated with hydrogen.
    • This is in contrast to alkenes and alkynes, which contain double and triple bonds and are known as unsaturated hydrocarbons.
    • Alkanes are named with the suffix "-ane" following the hydrocarbon prefixes.

  • Properties of Aromatic Compounds

    • Aromatic compounds, originally named because of their fragrant properties, are unsaturated hydrocarbon ring structures that exhibit special properties, including unusual stability, due to their aromaticity.
    • Poly-aromatic hydrocarbons are components of atmospheric pollution and are known carcinogens.

  • Reactions of Alkenes and Alkynes

    • Unsaturated hydrocarbons can participate in a number of different addition reactions across their double or triple bonds.

  • Other Aromatic Compounds

    • Many unsaturated cyclic compounds have exceptional properties that we now consider characteristic of "aromatic" systems.The following cases are illustrative:
    • Furan and pyrrole react more rapidly with bromine, but they also give substitution products.This tendency to favor substitution rather than addition suggests that the parent unsaturated ring system has exceptional stability.
    • The first example is azulene, a blue-colored 10 π-electron aromatic hydrocarbon isomeric with naphthalene.
    • Remarkably, this hydrocarbon is chemically unstable, in contrast to most other aromatic hydrocarbons.
    • Formulation of the Hückel rule prompted organic chemists to consider the possible aromaticity of many unusual unsaturated hydrocarbons.

  • Irreversible Addition Reactions

    • If substituent Y is a hydrogen, an alkyl group or an aryl group, the resulting alcohol is a stable compound and does not decompose with loss of hydrogen or hydrocarbons, even on heating.
    • Reduction of α,β-unsaturated ketones by metal hydride reagents sometimes leads to a saturated alcohol, especially with sodium borohydride.
    • These reagents are powerful nucleophiles and very strong bases (pKa's of saturated hydrocarbons range from 42 to 50), so they bond readily to carbonyl carbon atoms, giving alkoxide salts of lithium or magnesium.

  • Benzene and other Aromatic Compounds

    • Benzoic acid was eventually converted to the stable hydrocarbon benzene, C6H6, which also proved unreactive to common double bond transformations, as shown below.
    • The conceptual contradiction presented by a high degree of unsaturation (low H:C ratio) and high chemical stability for benzene and related compounds remained an unsolved puzzle for many years.

  • Characteristics of Mass Spectra

    • The small m/z=39 ion in propane and the absence of a m/z=29 ion in cyclopropane are particularly significant in distinguishing these hydrocarbons.
    • The unsaturated ketone, 4-methyl-3-pentene-2-one, on the left has no nitrogen so the mass of the molecular ion (m/z = 98) is an even number.