functional group: an atom, or group of atoms (with specific connectivity), exhibiting identical chemical reactivity regardless of the molecule containing it; the reactivity of individual functional groups dictates the reactivity of the molecule of which they are a part
- divide organic compounds into classes
- sites of characteristic chemical reactions
- serve as basis for naming organic compounds
- Contain only single carbon-carbon bonds (C-C). Because of this, they are considered “saturated” with hydrogen. General formula: CnH 2n+2
- Examples include methane, ethane, propane, and so on. Alkanes end in –ane.
- Alkanes are generally unreactive. They can be formed by the hydrogenation of alkenes, or in the Wolff-Kishner Reduction of aldehydes/ketones.
- contain only carbon-carbon and carbon-hydrogen single bonds
- Have at least one double carbon-carbon bond (C=C). Alkenes end in –ene.
- General formula: CnH2n .
- Also known as “olefins”
- They are much more reactive than alkanes, formed in elimination reaction of alcohols or alkyl halides. In the Wittig Reaction, alkenes are formed from aldehydes and ketones.
- contain a carbon-carbon double bond
- Have a carbon-carbon triple bond (C≡C). Their names end in –yne, like ethyne and propyne.
- General formula: CnH2n-2.
- Alkynes can be hydrogenated to form alkenes. They are formed from aldehydes in the Corey-Fuchs reaction.
- contain a carbon-carbon triple bond
- Containan –OH (“hydroxyl”) group bonded to a tetrahedral carbon atom
- Contain an oxygen atom bonded to hydrogen (O-H, or hydroxyl, group).
- Alcohols end in –ol. Examples include methanol (CH3OH), ethanol (found in alcoholic beverages), and butanol.
- Alcohols participate in many reactions: they are oxidized into carboxylic acids and ketones, and they are dehydrated to form alkenes.
- Contain an oxygen atom that is bonded to two carbon atoms (R-O-R).
- Ethers were originally used as anesthetics, particularly the dimethyl ether (CH3OCH3).
- Ethers are formed in the Williamson Synthesis from alkyl halides and alcohols.
- contain an oxygen atom bonded to two carbon atom groups by single bonds
- contain an “amino” group – a N atom bonded to 1, 2, or 3 carbon atom groups by single bonds
H. Aldehydes and Ketones
- contain a C=O (“carbonyl”) group
- note that in condensed structural formulas, the aldehyde group may be written as –CH=O or as –CHO
- Have a “terminal” carbonyl group, meaning that the carbonyl is at the end of a carbon chain, or that the carbonyl carbon is bonded to hydrogen.
- The simplest aldehyde is formaldehyde (H2 C=O). Other aldehydes end in –al.
- When reacted with the Grignard reagent, aldehydes form tertiary alcohols.
- When mixed with the Tollens reagent, aldehydes form a silver mirror.
- Have a non-terminal carbonyl group, with the carbonyl carbon occurring inside the carbon chain.
- The simplest ketone is acetone, (CH3)2 C=O.
- Ketones do not react with the Tollens reagent.
- They can be formed by the oxidation of secondary alcohols.
I. Carboxylic Acids
- Consist of a carbon double bonded to oxygen and single bonded to a hydroxyl (-OH) group. The carboxyl group is usually written –COOH.
- Per their name, carboxylic acids are acidic; examples include acetic acid (CH3 COOH). The simplest carboxylic acid is formic acid, HCOOH, which is found in ant venom.
- They are formed from aldehydes in the Cannizzaro Reaction.
- contain a “carboxylic acid” group – a carbonyl (C=O) group bonded to a hydroxyl group at the carbonyl carbon atom
- note that in condensed structural formulas, the carboxylic acid group may be written as –COOH
J. Carboxylic Amides (Amides)
- contain an “amide” group – a carboxylic acid (-COOH) group where the -OH group is replaced with an amine
K. Carboxylic Esters (Esters)
- Contain a carbon double bonded to one oxygen, and single bonded to another (a carbonyl group bonded to oxygen). Formula: R-COO-R
- Esters smell fruity.
- Esters are commonly formed in the Fischer esterification, from treating a carboxylic acid with an alcohol. They also are used in the Claisen condensation.
- contain an “ester” group – a carboxylic acid (-COOH) group where the H atom is replaced with a carbon containing group
L. Carboxylic Anhydrides (Anhydrides)
- contain an “anhydride” group – an oxygen atom bonded to two C=O (“carbonyl”) groups
- contain a “cyano” group (C≡N) bonded to a carbon atom group (i.e., at the carbon atom of the cyano group)
Amines, Amides, and Nitriles:
- There are several nitrogen-containing function groups, but the most commonly encountered at the high school level are amines, amides, and nitriles.
- Amines consist of a nitrogen atom with a lone pair, or, essentially, ammonia with at least one hydrogen replaced with a carbon (N-R3 ).
- Amides consist of a nitrogen atom bonded to a carbonyl group (-NC=O).
- Nitriles consist of a nitrogen atom triple bonded to a carbon atom.