Q: How can you distinguish between a primary amine and a tertiary amine using IR spectroscopy?

Primary amines show a medium band at $$3500\ \text{cm}^{-1}$$, tertiary amines do not show bands in this region.

Q: Which IR absorption is characteristic of a carbonyl group ($$\mathrm{C}=\mathrm{O}$$)?

$$\approx 1700\ \text{cm}^{-1}$$

Q: Which formula is used to calculate the degree of unsaturation for a molecule?

$$\text{Degree of unsaturation} = \frac{2C + 2 + N - H - X}{2}$$

Q: Which of the following IR absorptions would indicate the presence of a nitro group ($$\mathrm{NO}_2$$)?

$$1540\ \text{cm}^{-1}$$ and $$1300\ \text{cm}^{-1}$$

Question 1

Which region of the electromagnetic spectrum is primarily used in infrared (IR) spectroscopy for organic compound identification?

Accepted Answer

Infrarrojo (infrared)

Question 2

What is the relationship between wavelength ($$\lambda) $$and energy ($$E) in $$electromagnetic radiation?

Accepted Answer

$$E is $$inversely proportional to $$\lambda$$

Question 3

Given the equation $$E = h
u = hC/\lambda$$, what does $$
u$$ represent?

Accepted Answer

Frequency

Question 4

Which of the following functional groups would show a strong, broad IR absorption around $$3400-3650\ 	ext{cm}^{-1}$$?

Accepted Answer

Alcohol

Question 5

A compound shows two strong IR bands at $$1820-1660\ 	ext{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Anhydride

Question 6

How can you distinguish between a primary amine and a tertiary amine using IR spectroscopy?

Accepted Answer

Primary amines show a medium band at $$3500\ 	ext{cm}^{-1}$$, tertiary amines do not show bands in this region.

Question 7

Calculate the degree of unsaturation for a compound with the formula $$\mathrm{C}_5\mathrm{H}_8\mathrm{Cl}_2.$$

Accepted Answer

2

Question 8

Which IR absorption is characteristic of a carbonyl group ($$\mathrm{C}=\mathrm{O}$$)?

Accepted Answer

$$\approx 1700\ 	ext{cm}^{-1}$$

Question 9

A molecule has the formula $$\mathrm{C}_7\mathrm{H}_{14}\mathrm{O}_2. $$What is its degree of unsaturation?

Accepted Answer

1

Question 10

Which of the following statements about IR spectra is TRUE?

Accepted Answer

IR spectra can be used as a fingerprint to identify compounds.

Question 11

A compound shows a strong, broad IR absorption at $$2500-3100\ 	ext{cm}^{-1}$$ and a strong band at $$1700\ 	ext{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Carboxylic acid

Question 12

Which formula is used to calculate the degree of unsaturation for a molecule?

Accepted Answer

$$	ext{Degree of unsaturation} = \frac{2C + 2 + N - H - X}{2}$$

Question 13

Which of the following IR absorptions would indicate the presence of a nitrile group ($$\mathrm{C} \equiv \mathrm{N}$$)?

Accepted Answer

$$2210-2260\ 	ext{cm}^{-1}$$

Question 14

A student observes a strong IR band at $$1200\ 	ext{cm}^{-1}. $$Which functional group is most likely responsible?

Accepted Answer

Ether

Question 15

Which of the following best describes the effect of increasing frequency ($$
u) on $$the energy ($$E) of $$electromagnetic radiation?

Accepted Answer

Energy increases as frequency increases.

Question 16

Which IR region would you examine to identify the presence of aromatic rings?

Accepted Answer

$$1650-1450\ 	ext{cm}^{-1}$$

Question 17

A compound has the formula $$\mathrm{C}_4\mathrm{H}_6\mathrm{Br}_2. $$What is its degree of unsaturation?

Accepted Answer

2

Question 18

Which of the following is NOT a typical use of IR spectroscopy in organic chemistry?

Accepted Answer

Determining molecular weight

Question 19

Which of the following IR absorptions would indicate the presence of a nitro group ($$\mathrm{NO}_2$$)?

Accepted Answer

$$1540\ 	ext{cm}^{-1}$$ and $$1300\ 	ext{cm}^{-1}$$

Infrared Spectroscopy: Principles, Functional Groups, and Molecular Analysis

Study Guide - Practice Questions

Study Guide - Flashcards