Question 1

Which of the following best explains why the protons in CH$$_3CH=$$CHCl show different $$^1H $$NMR signals?

Accepted Answer

The proximity to electronegative chlorine causes different shielding, leading to distinct NMR signals for protons.

Question 2

A compound with the molecular formula C$$_4H$_{10}$$ shows 3 signals in its $$^1H $$NMR spectrum. What does this indicate about the molecule's symmetry?

Accepted Answer

The molecule has some symmetry.

Question 3

Given the following $$^1H $$NMR chemical shifts for PhCHClCH$$_2Cl$$: H$$_a (4.2 $$ppm), H$$_b (4.2 $$ppm), H$$_c (7.2 $$ppm), H$$_d (5.0 $$ppm), H$$_e (3.6 $$ppm), H$$_f (3.6 $$ppm), which protons are diastereotopic?

Accepted Answer

H$$_d$$ and H$$_f$$

Question 4

For vinyl bromide (CH$$_2=$$CHBr), which protons are diastereotopic and what are their approximate chemical shifts?

Accepted Answer

H$$_b$$ and H$$_c$$; 2.3 ppm and 3.4 ppm

Question 5

A $$^1H $$NMR spectrum shows a signal at 4.50 ppm with a complex splitting pattern for the hydrogen indicated in red in the following structure: $$\mathrm{(CH_3$)_2CHCOH}. $$What does this splitting pattern most likely indicate?

Accepted Answer

The hydrogen is coupled to three non-equivalent protons.

Question 6

Which DEPT sequence would you expect for the following molecule: $$\mathrm{CH_3CH_2CO_2CH(CH_3$)_2}$$, and what does it reveal about the types of carbons present?

Accepted Answer

DEPT-90 shows only CH carbons; DEPT-135 shows CH and CH$$_3 as $$positive, CH$$_2 as $$negative.

Question 7

A $$^{13}C $$NMR spectrum of a compound shows 7 signals. The DEPT-90 spectrum shows 2 signals, and the DEPT-135 spectrum shows 5 positive and 1 negative signal. What can you conclude about the structure?

Accepted Answer

There are 2 CH, 1 CH$$_2$$, 3 CH$$_3$$, and 1 quaternary carbon.

Question 8

Which of the following statements about diastereotopic protons is correct?

Accepted Answer

Diastereotopic protons have different chemical shifts and can show different coupling patterns.

Question 9

A molecule with the formula C$$_4H$_{10}$$ shows only one signal in its $$^1H $$NMR spectrum. Which structure is most likely?

Accepted Answer

Isobutane (2-methylpropane)

Question 10

In a $$^1H $$NMR spectrum, a signal at 7.2 ppm is most likely due to which type of proton?

Accepted Answer

Aromatic proton

Question 11

Which of the following best describes the effect of an electronegative atom (such as Cl) on the chemical shift of nearby protons in $$^1H $$NMR?

Accepted Answer

It causes downfield shifts due to decreased shielding.

Question 12

A $$^1H $$NMR spectrum of a compound shows a doublet at 1.2 ppm and a septet at 2.8 ppm. Which structure is most consistent with this data?

Accepted Answer

Isopropyl group ($$\mathrm{(CH_3$)_2CH-})$$

Question 13

Which of the following is true about the number of $$^1H $$NMR signals for a molecule with a plane of symmetry?

Accepted Answer

The number of signals decreases due to equivalent environments.

Question 14

A $$^1H $$NMR signal at 9-10 ppm is most likely due to which functional group?

Accepted Answer

Aldehyde

Question 15

Which of the following best describes the splitting pattern for a CH$$_2$$ group adjacent to a CH$$_3$$ group in $$^1H $$NMR?

Accepted Answer

Quartet

Question 16

A molecule shows a $$^1H $$NMR signal at 2.5 ppm as a singlet. Which of the following is the most likely environment for this proton?

Accepted Answer

Methyl group attached to a carbonyl (acetone)

Organic Chemistry NMR Exam Study Guidance

Guida di studio - Domande di pratica

Study guide - Flashcard