Splitting of a signal in a proton NMR spectrum tells us the number of chemically

Question

Splitting of a signal in a proton NMR spectrum tells us the number of chemically non-equivalent hydrogens in the immediate vicinity of the hydrogen giving the signal. Predict the number of lines exhibited by hydrogens at the labeled positions in a first-order NMR spectrum. (Make the approximation that all coupling constants are equal.) 1) The number of lines exhibited by hydrogen(s) a is 3 The number of lines exhibited by hydrogen(s) b is 4 The number of lines exhibited by hydrogen(s) cis1 2) The number of lines exhibited by hydrogen(s) a is The number of lines exhibited by hydrogen(s) b is 3 The number of lines exhibited by hydrogen(s) c is 9

Explanation / Answer

1)

The number of lines exhibited by hydrogen a is: 3

The number of lines exhibited by hydrogen b is: 4

The number of lines exhibited by hydrogen c is: 1

For hydrogen a; n = 2 so n+1 = 2+1 = 3

for hydrogen b; n = 3; n+1 = 3+1 = 4

for hydrogen c; n = 0; n+1 = 0+1= 1

2)

The number of lines exhibited by hydrogen a is: 1

The number of lines exhibited by hydrogen b is: 3

The number of lines exhibited by hydrogen c is: 9

Explanation: The number of lines is determined by n+1 rule. where, n = number of hydrogens attached to adjacent carbon atom.

For hydrogen a; n = 0 so n+1 = 0+1 = 1

for hydrogen b; n = 2; n+1 = 2+1 = 3

for hydrogen c; (n+1)(n+1) = (2+1)(2+1) = 3(3) = 9

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