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Grade: 12

                        

> Carboxylic acids and their derivatives 1 ) Decarboxylation reaction (WITH SODA-LIME OF b -keto carboxylic acid) 2) Arndt-Eistert rxn (mechanism, reference O.P Tendon-organic chemistry, rxn is for higher homologues of the acids) 3) Hunsdiecker rxn (bromo-becarboxylation, mechanisms) 4) rxn of acyl chloride with ammonia and amines(refer eg.benzoyl chloride + piperidine à N-Benzoylpiperidine) 5)Base hydrolysis of the ester (B AC 2; when ethyl propanoate labeled with 18 O in the ether type of oxygen of the ester is subjected to hydrolysis with aq.NaOH all of the 18 O shows up in ethanol that is produced,none of the 18 O appears in propanoate ions.why?; why here the attack at alkyl carbon not observed?) 6) In acid anhydrides,under heating effects of hydroxy acids,why b -hydroxy acid only forms a,b -unsaturated acid while other form( a,g,d) cyclic structures? 7) Why Clemmensen reduction is not used for compounds which have acid sensitive group, how to identify them? Similiarly, with Wolff-kishner reduction, we neglect base sensitive groups? 8) When to see for chair form or boat form of 6 membered ring & why is chair form less stable than boat form? 9) Please explain with mechanism of E1 reaction of alcohols, ethers; E2 reaction of alkyl halide. Some problem on ring expansion when to see for that? What are the necessary conditions for ring expansions? And why only E1 shows this effect while E2 doesn’t? Ø amines 10) Curtius rearrangements (mechanism with explanation) 11) Schmidt rxn (mechanism involved) 12) Lossen rearrangement {reference Morrison boyld} (base catalyzed mechanism; its mechanism) 13) Hinsberg rxn (explain with example in the chapter from module) 14) Dieckmanns’ condensation (mechanism with a suitable example)

9 years ago

Answers : (1)

SAGAR SINGH - IIT DELHI
879 Points
							

Dear student,

Acyl Group Substitution

This is probably the single most important reaction of carboxylic acid derivatives. 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. For certain nucleophilic reagents the reaction may assume other names as well. If Nuc-H is water the reaction is often called hydrolysis, if Nuc–H is an alcohol the reaction is called alcoholysis, and for ammonia and amines it is called aminolysis.

Different carboxylic acid derivatives have very different reactivities, acyl chlorides and bromides being the most reactive and amides the least reactive, as noted in the following qualitatively ordered list. The change in reactivity is dramatic. In homogeneous solvent systems, reaction of acyl chlorides with water occurs rapidly, and does not require heating or catalysts. Amides, on the other hand, react with water only in the presence of strong acid or base catalysts and external heating.

Reactivity:   acyl halides > anhydrides >> esters ≈ acids >> amides

Because of these differences, the conversion of one type of acid derivative into another is generally restricted to those outlined in the following diagram. Methods for converting carboxylic acids into these derivatives were shown in a previous section, but the amide and anhydride preparations were not general and required strong heating. A better and more general anhydride synthesis can be achieved from acyl chlorides, and amides are easily made from any of the more reactive derivatives. Specific examples of these conversions will be displayed by clicking on the product formula. The carboxylic acids themselves are not an essential part of this diagram, although all the derivatives shown can be hydrolyzed to the carboxylic acid state (light blue formulas and reaction arrows). Base catalyzed hydrolysis produces carboxylate salts.

9 years ago
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