Q18P - Organic Chemistry (Mcmurry)

Question

Propose structures for compounds that fit the following descriptions: 

(a) A hydrocarbon with seven lines in its ¹³C NMR spectrum 

(b) A six-carbon compound with only five lines in its ¹³C NMR spectrum 

(c) A four-carbon compound with three lines in its ¹³C NMR spectrum

Step-by-Step Solution

Answer

Most ¹³C resonances are between 0 and 220 ppm downfield from the TMS reference line, with the exact chemical shift of each ¹³C resonance dependent on that carbon’s electronic environment within the molecule.

 

Generally, the chemical shift is affected by the electronegativity of a nearby atom like oxygen, nitrogen, halogen, etc.

Step 1: 13 C NMR spectroscopy

Most ¹³C resonances are between 0 and 220 ppm downfield from the TMS reference line, with the exact chemical shift of each ¹³C resonance dependent on that carbon’s electronic environment within the molecule.

Generally, the chemical shift is affected by the electronegativity of a nearby atom like oxygen, nitrogen, halogen, etc.

Step 2: Structure of a hydrocarbon with seven lines in its 13 C NMR spectrum

By using the above information we can conclude that we have to draw the hydrocarbon which gives seven lines in its ¹³CNMR spectra. So in the given structure, there are seven different types of carbon present which mean the environment for each carbon is different so it gives different signals.

So the structure is as follows;

Step 3: The structure of a six-carbon compound with only five lines in its 13 C NMR spectrum

By using the above information we can conclude that we have to draw the six-carbon compound which gives five lines in its ¹³CNMR spectra. So in the given structure, there are five different types of carbon present which mean the environment for two carbon is the same while for the other is different.

So the structure is as follows

Step 4: The structure of a four-carbon compound with three lines in its 13 C NMR spectrum

By using the above information we can conclude that we have to draw the four-carbon compound which gives three lines in its ¹³CNMR spectra. So in the given structure, there are three different types of carbon present which mean the environment for two carbon is the same while for the other is different.

So the structure is as follows;