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7.3: Functional groups

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    538685

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    Learning Objectives
    • Define organic functional group and recognize it in an organic compound.

    What is a functional group?

    A functional group is an atom or a group of atoms that imparts a characteristic set of physical and chemical properties to the compound.

    For example, alkanes with no functional group are the least reactive classes of organic compounds. Alkanes have only \(\ce{C-C}\) and \(\ce{C-H}\) single bonds, which are nonpolar and strong bonds. Alkenes, alkynes, and aromatic compounds are relatively reactive classes of organic compounds because they have a \(\ce{C=C}\) bond, \(\ce{C≡C}\) bond, or a benzene ring as functional groups. Although alkenes, alkynes, and aromatic hydrocarbons are nonpolar, there is a partial negative (\(\delta^{-}\)) character in the \(\pi\)-bond region that attracts electrophilic reagents having \(\delta^{+}\) regions. Further, the \(\pi\)-bond is weaker than a \(\sigma\)-bond making it easier to break during chemical reactions.

    Classification of organic compounds based on the functional groups

    One primary class of organic compounds is hydrocarbons that contain only \(\ce{C's}\) and \(\ce{H's}\), listed in Table 1, and the others are organic compounds with heteroatom/s, in their functional group/s. Hydrocarbons have been introduced in the previous section. Other classes of organic compounds containing heteratom\s in their functional groups are described next.

    The heteroatom/s in the functional group can be a single bonded, i.e., sp3-hybridized halogen, \(\ce{O}\), \(\ce{N}\), \(\ce{S}\), \(\ce{P}\), etc., listed in Table 2; a double bonded, i.e., sp2-hybridized \(\ce{O}\), \(\ce{N}\), \(\ce{S}\), \(\ce{P}\), etc., listed in Table 3; or a combination of these, listed in Table 4.

    Table 1: Major Functional Classes of organic moleculse. (R-, R1-, R2, R3, and R4- represents a general alkyl group or hydrogen)
    Class name Group name General structural formula General condensed formula Prefix Suffix Example
    Alkane Alkyl R R alkyl- -ane clipboard_e32b1f3e01d95eb033db35d1cd57c4110.png
    Alkene Alkenyl clipboard_e6da5b33775d36ad775074efabad1ce5e.png \(\ce{R2C=CR2}\) alkenyl- -ene clipboard_e4276d5febdfb880d024c2b6b714bb7df.png
    Alkyne Alkynyl clipboard_ea3831a752cf209b5c46589e57fbe29eb.png \(\ce{RC≡CR2}\) alkynyl- -yne clipboard_e4fad3ad3830e8bd4a95df50a5cb57079.png
    Aromatic (benzene derivatives) Phenyl clipboard_ec768d43d0fbeabc462ebe2bda38b6e3f.png \(\ce{R-C6H5}\) phenyl- -benzene clipboard_ef4149332a22f6ce8d3a9d8c5d7f2347a.png
    Haloalkane Halo \(\ce{R-X}\), i.e., \(\ce{R-F}\), \(\ce{R-Cl}\), \(\ce{R-Br}\), or \(\ce{R-I}\) \(\ce{R-X}\) i.e., \(\ce{R-F}\), \(\ce{R-Cl}\), \(\ce{R-Br}\), or \(\ce{R-I}\) halo- i.e., fluoro-, chloro-, bromo-, or iodo-) - \(\ce{CH3-CH2-Cl}\) (chloroethane)
    Alcohol Alcohol \(\ce{R-OH}\) \(\ce{ROH}\) hydroxy- -ol \(\ce{CH3-CH2-OH}\) (ethanol)
    Ether Ether \(\ce{R-O-R'}\) \(\ce{ROR'}\) Alkoxy - \(\ce{CH3-CH2-O-CH2-CH3}\) (ethoxyethane)
    Amine Amine clipboard_e4f862ed62da2d8f94094cd9c58741218.png \(\ce{R1R2R3N}\) amino- -amine clipboard_e2eb24c1f57f8f621484668a6f05a2f7c.png
    Aldehyde Aldehyde clipboard_e0cf270ba48d9db1f93d6a4c40532a554.png \(\ce{RCHO}\) oxo- -al clipboard_ed8638516b637348798a79d0b31dffd66.png
    Ketone Ketone clipboard_e20fd24f94b9dd0186acf82365e9c0cbc.png \(\ce{RCOR'}\) oxo- -one clipboard_ef6563f776f19d93af918a4ba18ecf554.png
    Carboxylic acid Carboxyl clipboard_edc35c3f02f14964c205aa1672407690e.png \(\ce{R-COOH}\) carboxy- oic acid clipboard_e8455ee13e52aa59264dd361ba772ceba.png

    This page titled 7.3: Functional groups was last modified on Tue, 16 Dec 2025 03:18:15 GMT and is shared under a Public Domain license and was authored, remixed, and/or curated by Seth Yates.