13^C NMR

Question 1

What is the general range of 13^C spectroscopy?

Answer 1

0 delta - 220 delta

Question 2

SP3 carbons of alkyl groups are _________.

Answer 2

Shielded (0-90)

Question 3

SP2 carbons of Alkenes and benzene rings are ____________.

Answer 3

De-shielded (110-220)

Question 4

Carbonyl carbons are ___________.

Answer 4

Highly deshielded (160-220)

Question 5

Unlike H NMR, I’m C NMR, the absorption signals are…….

Answer 5

Not split by neighboring carbon atoms. As a result, peak intensities are not proportional to the number of carbon atoms that give rise to them. C NMR is not integrated.

Question 6

C NMR can be used in what two major ways?

Answer 6

-to identify the structure of an unknown or the products of a chemical reaction
-to support a reaction mechanism
Ex: confirmation of Zaytsev rule.

Question 7

What are the three steps of experimental procedure in DEPT C NMR?

Answer 7

• broad band decoupled (BBD)
• DEPT-90 Spectrum
• DEPT-135

Question 8

In broad band decoupled (BBD) Spectrum, signals of all carbon groups present in the compound appear as ________ signals.

Answer 8

Positive

Question 9

I’m DEPT-90 Spectrum shows only signals of all _____ groups present in the compound.

Answer 9

CH

Question 10

DEPT-135 Spectrum shows all CH, CH3 groups present as _________ signals, and all CH2 groups as ________ signals.

Answer 10

Positive

Negative

Question 11

Why is there no carbon-carbon coupling in 13^C NMR?

Answer 11

It is rare to have two carbon 13 next to each other (low abundance of carbon 13)

Question 12

Why is there no carbon-hydrogen coupling?

Answer 12

There is carbon hydrogen coupling however, the instrument uses “broad band decoupling” to suppress it.