Q13-20P - Organic Chemistry (Mcmurry)

Question

Assign a chemical shift to each carbon in 6-methyl-5-hepten-2-ol.

Step-by-Step Solution

Answer

The chemical shift for carbon-1 is 23.26$\mathrm{\delta }$.

The chemical shift for carbon-2 is 132$\mathrm{\delta }$.

The chemical shift for carbon-3 is 124$\mathrm{\delta }$. 

The chemical shift for carbon-4 is 39$\mathrm{\delta }$. 

The chemical shift for carbon-5 is 24$\mathrm{\delta }$. 

The chemical shift for carbon-6 is 68$\mathrm{\delta }$. 

The chemical shift for carbon-7 is 18$\mathrm{\delta }$. 

Step 1: Definition of chemical shift

Chemical shift is the shift in absorption which is expressed in terms of some standard reference compound which is TMS.

TMS has a chemical shift value of 0 ppm.

Actually, there are two different factors that cause the chemical shift which is shielding and deshielding.

Step 2: Chemical shift in 6-methyl-5-hepten-2-ol

The structure of 6-methylhept-5-en-2-ol is as follows:

The carbon NMR shows 8 peaks which correspond to each carbon in the molecule. The most downfield peak will be assigned first. The peak is around 130-132 delta units which are typical for $\text{C=C}$ bond. Because the second carbon is attached to two methyl groups, it is less shielded and thus more downfield.

The chemical shift for carbon-1 is 23.26$\mathrm{\delta }$.

The chemical shift for carbon-2 is 132$\mathrm{\delta }$.

The chemical shift for carbon-3 is 124$\mathrm{\delta }$. 

The chemical shift for carbon-4 is 39$\mathrm{\delta }$. 

The chemical shift for carbon-5 is 24$\mathrm{\delta }$. 

The chemical shift for carbon-6 is 68$\mathrm{\delta }$. 

The chemical shift for carbon-7 is 18$\mathrm{\delta }$.