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Dolbier HW Solutions 434 - along with a dihydroxy...

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19.27 Examination of the molecular formula C 14 H 26 O 2 reveals that the compound has an index of hydrogen de fi ciency of 2. Because we are told that the compound is a carboxylic acid, one of these elements of unsaturation must be a carbon oxygen double bond. The other must be a carbon carbon double bond because the compound undergoes cleavage on ozonolysis. Examining the products of ozonol- ysis serves to locate the position of the double bond. The starting acid must be 5-tetradecenoic acid. The stereochemistry of the double bond is not re- vealed by these experiments. 19.28 Hydrogenation of the starting material is expected to result in reduction of the ketone carbonyl while leaving the carboxyl group unaffected. Because the isolated product lacks a carboxyl group, how- ever, that group must react in some way. The most reasonable reaction is intramolecular esteri fi ca- tion to form a -lactone. 19.29 Compound A is a cyclic acetal and undergoes hydrolysis in aqueous acid to produce acetaldehyde,
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Unformatted text preview: along with a dihydroxy carboxylic acid. The dihydroxy acid that is formed in this step cyclizes to the d-lactone mevalonolactone. 19.30 Compound A is a d-lactone. To determine its precursor, disconnect the ester linkage to a hydroxy acid. Compound A O H H CH 3 O H H CH 3 CO 2 H OH 3,5-Dihydroxy-3-methylpentanoic acid CH 3 CH 2 CO 2 H HO OH HO HO CH 2 O CH 3 OH Mevalonolactone O CH 3 OH O ; Compound A 3,5-Dihydroxy-3-methylpentanoic acid Acetaldehyde H 3 O 1 O O CH 3 CH 3 CH 2 CO 2 H CH 3 CH 2 CO 2 H HO OH O CH 3 CH 1 Levulinic acid 4-Hydroxypentanoic acid (not isolated) 4-Pentanolide (C 5 H 8 O 2 ) H 2 , Ni O O H 3 C CH 3 CHCH 2 CH 2 COH OH O CH 3 CCH 2 CH 2 COH O O CH 3 (CH 2 ) 7 CH HC(CH 2 ) 3 CO 2 H Cleavage by ozone occurs here. Nonanal 5-Oxopentanoic acid CH 3 (CH 2 ) 7 CH CH(CH 2 ) 3 CO 2 H 1. O 3 2. H 2 O, Zn 1 O O 528 CARBOXYLIC ACIDS __ __ __...
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