Q41P For each compound shown below,Sk... [FREE SOLUTION]

Chapter 13: Q41P (page 702)

For each compound shown below,
Sketch the ${}^{13}C$ NMR spectrum (totally decoupled, with a singlet for each type of carbon), showing approximate chemical shifts.
Show the multiplicity expected for each signal in the off-resonance-decoupled spectrum.
Sketch the spectra expected using the DEPT-90 and DEPT-135 techniques.

Short Answer

Expert verified

Answer. 1. and 2.

${}^{13}C$ NMR spectrums for the given molecules have been sketched and multiplicities have been assigned along with chemical shift values in the spectrum. 鈥渟鈥� means singlet, 鈥渄鈥� means doublet, 鈥渢鈥� means triplet and 鈥渜鈥� means quartet.

Splitting multiplicity has been written in italic alphabets so as to avoid confusion.

Spin-multiplicity has been written in italic alphabets so as to avoid confusion.

Answer 3.DEPT-90 and DEPT-135 spectra for the given molecules have been sketched.

The DEPT-90 spectrum for ethyl acetate would have no peaks because there are no methine groups.

The DEPT-90 spectrum would have no peaks because there are no methine groups in molecule (d).

Step by step solution

Step-1. Explanation of part (1), (2) and (3) of molecule (a) ethyl acetate:

Distortionless Enhancement by Polarization Transfer (DEPT) is a double resonance pulse program that transfers polarization from an excited nucleus to another. There are three DEPT experiments and they differ only in the 鈥淎PT portion鈥� of the pulse program, meaning, that they differ only in magnitude of the final $1 H$ tip angle (X = 45, 90, 130). DEPT-45 leaves all resonances with a positive phase, DEPT-90 only shows methine carbon and DEPT-135 shows methine/methyl with a positive phase and methylene with a negative phase.

In molecule (a), the multiplicities in the off-resonance decoupled spectrum are indicated with chemical shift values and DEPT-135 spectrum have been drawn. In DEPT-135 spectrum, since there are two methyl groups in ethyl acetate, thus they are shown as upwards peak and there is only one methylene group in ethyl acetate, thus, its peak is shown downwards. The DEPT-90 spectrum for ethyl acetate would have no peaks because there are no methine groups.

Carbon-NMR spectrum and DEPT spectrum for molecule (a)

Step-2. Explanation of part (1), (2) and (3) of molecule (b) 3-chloroprene:

In molecule (b), the multiplicities in the off-resonance decoupled spectrum are indicated with chemical shift values and DEPT-135 and DEPT-90 spectrums have been drawn. In DEPT-135 spectrum, since there is one methine group in 3-chloropropene, thus it is shown as upwards peak and there are two methylene groups in 3-chloropropene, their peak is shown downwards. The DEPT-90 spectrum for 3-chloroprene would have one upward peak as there is only one methine carbon.

Carbon-NMR spectrum and DEPT spectrum for molecule (b)

Step-3. Explanation of part (1), (2) and (3) of molecule (c):

In molecule (c), the multiplicities in the off-resonance decoupled spectrum are indicated with chemical shift values and DEPT-90 and DEPT-135 spectrums have been drawn. In DEPT-135 spectrum, since there are two methylene groups in the structure, thus they are shown as downwards peak and there are two methine groups in structure, thus, their peak is shown upwards. The DEPT-90 spectrum for molecule (c) would have two upwards peak as there are two methine groups present.

Carbon-NMR spectrum and DEPT spectrum for molecule (c)

Step-4. Explanation of part (1), (2) and (3) of molecule (d):

Distortionless Enhancement by Polarization Transfer (DEPT) is a double resonance pulse program that transfers polarization from an excited nucleus to another.There are three DEPT experiments and they differ only in the 鈥淎PT portion鈥� of the pulse program, meaning, that they differ only in magnitude of the final $1 H$ tip angle (X = 45, 90, 130). DEPT-45 leaves all resonances with a positive phase, DEPT-90 only shows methine carbon and DEPT-135 shows methine/methyl with a positive phase and methylene with a negative phase.

In molecule (d), the multiplicities in the off-resonance decoupled spectrum are indicated with chemical shift values and DEPT-135 spectrum have been drawn. In DEPT-135 spectrum, since there are two methyl groups in structure, thus they are shown as upwards peak and there is only one methylene group, thus, its peak is shown downwards. The DEPT-90 spectrum for molecule (d) would have no peaks because there are no methine groups.