Q: Which of the following statements about the IR spectrum of an alkyne is correct?

It shows a sharp absorption near $$2250 \, \text{cm}^{-1}$$ due to $$\ce{C#C}$$ stretch.

Q: Which of the following statements about the fingerprint region in IR spectroscopy is correct?

It is unique for each molecule and found below $$1500 \, \text{cm}^{-1}.$$

Question 1

Which of the following IR absorption bands is most characteristic of a carbonyl (C=O) group in a simple ketone?

Accepted Answer

$$1715 \, 	ext{cm}^{-1}$$

Question 2

A compound with the molecular formula $$C_4H_8O$$ shows a strong, broad IR absorption at $$3300 \, 	ext{cm}^{-1}$$ and no significant absorption near $$1715 \, 	ext{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Alcohol

Question 3

What is the Index of Hydrogen Deficiency (IHD) for a compound with the formula $$C_6H_6$$?

Accepted Answer

4

Question 4

Which of the following statements about the IR spectrum of an alkyne is correct?

Accepted Answer

It shows a sharp absorption near $$2250 \, 	ext{cm}^{-1}$$ due to $$\ce{C#C}$$ stretch.

Question 5

A compound with the formula $$C_3H_8O$$ shows a broad IR absorption at $$3300 \, 	ext{cm}^{-1}$$ and an NMR singlet at $$2.9$$ ppm integrating for 1H. What is the most likely structure?

Accepted Answer

2-Propanol

Question 6

Which of the following NMR chemical shifts is most consistent with a methyl group attached to a carbonyl ($$\ce{$$COCH_3$$}$$)?

Accepted Answer

$$2.1$$ ppm

Question 7

A molecule with the formula $$C_5H_8$$ has how many degrees of unsaturation?

Accepted Answer

2

Question 8

Which IR absorption would you expect to be absent in the spectrum of a pure hydrocarbon alkane?

Accepted Answer

$$1715 \, 	ext{cm}^{-1}$$

Question 9

A compound with the formula $$C_4H_7Br$$ has how many degrees of unsaturation?

Accepted Answer

1

Question 10

Which of the following is a correct interpretation of a septet at $$3.7$$ ppm in a $$^1H $$NMR spectrum?

Accepted Answer

A proton adjacent to six equivalent protons

Question 11

Which functional group is indicated by a strong, broad IR absorption around $$2500$$–$$3300 \, 	ext{cm}^{-1}$$ and a strong absorption near $$1710 \, 	ext{cm}^{-1}$$?

Accepted Answer

Carboxylic acid

Question 12

A $$^1H $$NMR spectrum shows three signals: a doublet integrating for 6H at $$1.1$$ ppm, a septet integrating for 1H at $$3.7$$ ppm, and a broad singlet at $$2.9$$ ppm. Which structure best fits this data?

Accepted Answer

2-Propanol

Question 13

Which of the following statements about the fingerprint region in IR spectroscopy is correct?

Accepted Answer

It is unique for each molecule and found below $$1500 \, 	ext{cm}^{-1}.$$

Question 14

Which of the following is NOT considered when calculating the Index of Hydrogen Deficiency (IHD)?

Accepted Answer

Oxygen atoms

Question 15

A compound with the formula $$C_6H_7N$$ has how many degrees of unsaturation?

Accepted Answer

4

Question 16

Which of the following IR absorptions would indicate the presence of a nitrile group?

Accepted Answer

$$2250 \, 	ext{cm}^{-1}$$

Question 17

A $$^1H $$NMR spectrum shows a triplet at $$1.0$$ ppm and a quartet at $$2.4$$ ppm. What fragment is most likely present?

Accepted Answer

Ethyl group ($$\ce{CH_3CH_2-})$$

Question 18

Which of the following is a correct statement about the effect of conjugation on the IR absorption of a carbonyl group?

Accepted Answer

Conjugation lowers the frequency of the $$\ce{C=O}$$ stretch.

Spectral Analysis in Organic Chemistry: IR and NMR Interpretation Guide

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