acyl

(noun)

Any of class of organic radicals, RCO-, formed by the removal of a hydroxyl group from a carboxylic acid.

Related Terms

  • acetyl CoA
  • fatty acid

Examples of acyl in the following topics:

  • Acyl Group Substitution

    • The overall transformation is defined by the following equation, and may be classified either as nucleophilic substitution at an acyl group or as acylation of a nucleophile.
    • Reactivity: acyl halides > anhydrides >> esters ≈ acids >> amides
    • Before proceeding further, it is important to review the general mechanism by means of which all these acyl transfer or acylation reactions take place.
    • The first three examples concern reactions of acyl chlorides, the most reactive acylating reagents discussed here.
    • No acylation reactions of amides were shown in these problems.
  • Characteristics of Specific Substitution Reactions

    • The Friedel-Crafts acylation reagent is normally composed of an acyl halide or anhydride mixed with a Lewis acid catalyst such as AlCl3.
    • Some examples of Friedel-Crafts acylation reactions are shown in the following diagram.
    • The first demonstrates that unusual acylating agents may be used as reactants.
    • The second makes use of an anhydride acylating reagent, and the third illustrates the ease with which anisole reacts, as noted earlier.
    • Since the nitro group is a powerful deactivating substituent, Friedel-Crafts acylation of nitrobenzene does not take place under any conditions.
  • Reactions at the α-Carbon

    • Acyl halides and anhydrides are more easily halogenated than esters and nitriles, probably because of their higher enol concentration.
    • Thus, conversion of the acid to its acyl chloride derivative is followed by alpha-bromination or chlorination, and the resulting halogenated acyl chloride is then hydrolyzed to the carboxylic acid product.
    • This simple modification works well because carboxylic acids and acyl chlorides exchange functionality as the reaction progresses.
    • The final product is the alpha-halogenated acid, accompanied by a trace of the acyl halide.
    • To see a mechanism for the acyl halide-carboxylic acid exchange, view the second diagram below.
  • Oxidation of Alcohols by DMSO

    • Most of the electrophiles are good acylating reagents, so it is reasonable to expect an initial acylation of the sulfoxide oxygen.
    • (The use of DCC as an acylation reagent was described elsewhere. ) The electrophilic character of the sulfur atom is enhanced by acylation.
  • Fats & Oils

    • Triglycerides having three identical acyl chains, such as tristearin and triolein (above), are called "simple", while those composed of different acyl chains are called "mixed".
    • If the acyl chains at the end hydroxyl groups (1 & 3) of glycerol are different, the center carbon becomes a chiral center and enantiomeric configurations must be recognized.
  • The Configuration of Free Radicals

    • The following illustration shows the decomposition of a bicyclic bridgehead acyl peroxide.
    • The concurrent formation of ester and dimeric cycloalkane products from acyl peroxides is common, and reflects a cage effect in homolysis reactions.
  • Four-Membered Rings

    • Cleavage reactions of β-lactones may take place either by acid-catalyzed acyl exchange, as in 4a, or by alkyl-O rupture by nucleophiles, as in 4b.
    • Finally, the β-lactam cleavage of penicillin G (reaction 6) testifies to the enhanced acylating reactivity of this fused ring system.
    • Most amides are extremely unreactive acylation reagents, thanks to stabilization by p-π resonance.
  • Nomenclature

    • Three examples of acyl groups having specific names were noted earlier.
    • Esters: The alkyl group is named first, followed by a derived name for the acyl group, the oic or ic suffix in the acid name is replaced by ate. e.g.
    • Acid Halides: The acyl group is named first, followed by the halogen name as a separate word. e.g.
  • The Arndt-Eistert Reaction

    • The rearrangement of acyl nitrenes to isocyanates that is the crux of the Hofmann, Curtius and Lossen rearrangements, is paralleled by the rearrangement of acyl carbenes to ketenes, a transformation called the Wolff rearrangement.
    • The starting acid, written on the left, is converted first to an acyl chloride derivative, and then to a diazomethyl ketone.
  • Overview of Reducing Agents

    • In a similar sense, acyl chlorides are the most reactive substrate.
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