Allylic

Allylic refers to the position in an organic molecule that is adjacent to a carbon-carbon double bond. The term is derived from the word "allyl," which is the name of the substituent group with the formula H2C=CH-CH2-. The allylic position is significant in organic chemistry due to its unique reactivity and the stability of allylic intermediates.

Structure and Bonding

The allylic position is characterized by the presence of a carbon atom that is bonded to another carbon atom which is part of a double bond. This arrangement allows for the delocalization of electrons, which can stabilize certain intermediates such as allyl cations, allyl radicals, and allyl anions. The resonance structures of these intermediates contribute to their stability.

Reactivity

Allylic compounds exhibit unique reactivity patterns due to the stability of the allylic intermediates. Some common reactions involving allylic positions include:

• Allylic Substitution: In this reaction, a leaving group at the allylic position is replaced by a nucleophile. This can occur via an S_N1 or S_N2 mechanism, depending on the conditions.
• Allylic Oxidation: This reaction involves the oxidation of an allylic hydrogen to form an allylic alcohol or ketone. Common reagents for this transformation include selenium dioxide (SeO2) and manganese dioxide (MnO2).
• Allylic Rearrangement: This involves the migration of a substituent from one allylic position to another, often facilitated by the formation of a resonance-stabilized allylic intermediate.

Applications

Allylic compounds are important in various fields of chemistry and industry. They are used as intermediates in the synthesis of pharmaceuticals, polymers, and other organic compounds. The unique reactivity of allylic positions is exploited in many synthetic strategies to construct complex molecules.

Examples of Allylic Compounds

• Allyl chloride (H2C=CH-CH2Cl)
• Allyl alcohol (H2C=CH-CH2OH)
• Allyl bromide (H2C=CH-CH2Br)

Related Concepts

• Vinyl group
• Propargylic
• Benzylic
• Conjugation (chemistry)
• Resonance (chemistry)

See Also

• Organic chemistry
• Substitution reaction
• Oxidation
• Rearrangement reaction