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Deduce the structure of each compound from the information

Chapter 21, Problem 43SP

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QUESTION:

Problem 43SP

Deduce the structure of each compound from the information given. All unknowns in this problem have molecular formula C8H12.

a) Upon catalytic hydrogenation, unknown W gives cyclooctane. Ozonolysis of W, followed by reduction with dimethyl sulfide, gives octanedioic acid, HOOC—(CH2)6—COOH. Draw the structure of W.

(b) Upon catalytic hydrogenation, unknown X gives cyclooctane. Ozonolysis of X, followed by reduction with dimethyl sulfide, gives two equivalents of butanedial, O CH—CH2CH2—CH O. Draw the structure of X.

(c) Upon catalytic hydrogenation, unknown Y gives cyclooctane. Ozonolysis of Y, followed by reduction with dimethyl sulfide, gives a three-carbon dialdehyde and a five-carbon dialdehyde. Draw the structure of Y.

*(d) Upon catalytic hydrogenation, unknown Z gives cis-bicyclo[4.2.0]octane. Ozonolysis of Z,followed by reduction with dimethyl sulfide, gives a cyclobutane with a three-carbon aldehyde (—CH2—CH2—CHO) group on C1 and a one-carbon aldehyde (—CHO) group on C2. Draw the structure of Z.

Questions & Answers

QUESTION:

Problem 43SP

Deduce the structure of each compound from the information given. All unknowns in this problem have molecular formula C8H12.

a) Upon catalytic hydrogenation, unknown W gives cyclooctane. Ozonolysis of W, followed by reduction with dimethyl sulfide, gives octanedioic acid, HOOC—(CH2)6—COOH. Draw the structure of W.

(b) Upon catalytic hydrogenation, unknown X gives cyclooctane. Ozonolysis of X, followed by reduction with dimethyl sulfide, gives two equivalents of butanedial, O CH—CH2CH2—CH O. Draw the structure of X.

(c) Upon catalytic hydrogenation, unknown Y gives cyclooctane. Ozonolysis of Y, followed by reduction with dimethyl sulfide, gives a three-carbon dialdehyde and a five-carbon dialdehyde. Draw the structure of Y.

*(d) Upon catalytic hydrogenation, unknown Z gives cis-bicyclo[4.2.0]octane. Ozonolysis of Z,followed by reduction with dimethyl sulfide, gives a cyclobutane with a three-carbon aldehyde (—CH2—CH2—CHO) group on C1 and a one-carbon aldehyde (—CHO) group on C2. Draw the structure of Z.

ANSWER:

Answer :

a) We have to look at the molecular formula first .

A structure with 8 carbons and 12 hydrogens has 3 elements of unsaturation.since hydrogenation of this unknown molecule gives cyclooctane ,cyclooctyne is a possible match for the unknown starting material.

The ring would count as one element of saturation ,and the alkyne would account for other two.

For this to be correct it has to match the other data we have.We were told that ozonolysis /mild reduction with dimethyl sulfide led to an eight carbon dicarboxylic acid .so we know that ozonolysis of an alkyne splits the triple bond down the middle ,leaving each carbon fragment with a carboxylic acid group.treatment of cyclooctyne with ozone /DMS would indeed lead to octanedioic acid .This unknown is most likely cyclooctyne .

(b) Upon catalytic hydrogenation, unknown X gives cyclooctane. Ozonolysis of X, followed by reduction with dimethyl sulfide, gives two equivalents of butanedial, O CH—CH

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