Q13.48E - Organic Chemistry (Mcmurry)

Question

Suppose you ran a DEPT-135 spectrum for each substance in Problem

13-47. Which carbon atoms in each molecule would show positive

peaks, and which would show negative peaks?

Step-by-Step Solution

Answer

In the compound,1,1-dimethylcyclohexane, the carbon atom 1 gives positive peak and the carbon atom 3,4 and 5 give negative peaks.

In the compound ethyl methyl ether, carbon atoms one and three give positive peaks. The carbon atom two gives negative peak.

In the compound tert-butylcyclohexane, the carbon atoms 1 and 3 give positive peaks. The carbon atoms 4, 5 and 6 give negative peaks.

In the compound 3-methyl-1-pentyne, the carbon atoms one, three, five and six give positive peaks. The carbon atom 4 gives negative peaks.

In the compound cis-1,2-dimethylcyclohexane,the carbon atoms 1 and 2 give positive peaks. The carbon atoms 3 and 4 give negative peaks.

In the compound cyclohexanone, there is no positive peak. The carbon atoms two, three and four give negative peaks. 

Step 1: DEPT-135 spectrum

The DEPT-135 spectra provides the signal of all protonated carbons. The CH and signals are indicated positive and the -CH₂ signal is indicated as negative. The signal of quartenary carbons is not present in the DEPT spectrum. 

Step 2: The carbon atoms in each compound that show the positive and negative peaks

The CH and -CH₃ groups are positive in DEPT-135 spectrum and the -CH₂group is negative. In the compound,1,1-dimethylcyclohexane, the carbon atom 1 gives positive peak and the carbon atom 3,4 and 5 give negative peaks.

                               Structure of compound (a)

In the compound ethyl methyl ether, carbon atoms one and three give positive peaks. The carbon atom two gives negative peak.

                           Structure of compound (b)

In the compound tert-butylcyclohexane, the carbon atoms 1 and 3 give positive peaks. The carbon atoms 4, 5 and 6 give negative peaks.

                                     Structure of compound (c)

In the compound 3-methyl-1-pentyne, the carbon atoms one, three, five and six give positive peaks. The carbon atom 4 gives negative peaks.

                            Structure of compound (d)

In the compound cis-1,2-dimethylcyclohexane,the carbon atoms 1 and 2 give positive peaks. The carbon atoms 3 and 4 give negative peaks.

                                      Structure of compound (e)

In the compound cyclohexanone, there is no positive peak. The carbon atoms two, three and four give negative peaks. 

                                          Structure of compound (f)