Question

What is the difference between a regular 13C NMR and a 13C NMR registered in a proton coupled mode?

Answer 1

Requirement for NMR : Spin quantum #(I)#0

Meaning-must be an odd number and /or neutrons

Ex. ¹H ,²H ,¹³C ,¹⁹F etc

The ¹³C NMR is directly about the carbon skeleton not just the proton attached to it.

Proton coupled spectrum	Proton decoupled spectrum
a.) number of signal tell us how many different carbon or set of equivalent carbon present in sample	shows no splitting at all , it consists of single set of peak, one for each carbon or each set of carbon in the molecule , even for very complicated molecules ,such spectrum is amazingly simple (because overlapping multiplet very difficult to interpret .
b) The splitting of signal tell us how many hydrogen are attached to each other .(n+1)rule	for biomolecules proton decoupled 13 C NMR prefer over coupled spectrum .
c) The chemical shift tell us hybridization of carbon ( SP3 , SP2 , SP etc)  atom	chemical shift in 13C NMR arrive in same fashion to that of 1HNMR .
d) integration not useful for 13C NMR.	Particular carbon has individuals chemical shift based on type of hybridization and vicinity of electronegative atom .
Details = 13C - H coupling is possible but 13C -13C not possible due to natural abundance of carbon is very low (1.11%). Due to low natural abundance of carbon,  13C NMR spectrum does not possess carbon -carbon splitting .	This type of spectrum preferred over proton coupled because of its simplicity .