Question 1

Bending vibrations in the infared region occur at:

Accepted Answer

Bending vibrations typically occur at frequencies below 1400 cm^-1 in the infrared region. This range is characteristic of the energy required to bend molecular bonds rather than stretch them.

Question 2

The area in the infared spectrum between 1400 and 400 cm^-¹ is called the .

Accepted Answer

The area in the infrared spectrum between 1400 and 400 cm^-1 is known as the fingerprint region. This region is unique for most organic compounds and is used to identify or distinguish between different substances.

Question 3

Which bond would show a sharp absorption in the IR between 3000 and 2800 cm^-¹?

Accepted Answer

C-H bonds show a sharp absorption in the IR spectrum between 3000 and 2800 cm^-1, which is characteristic of alkanes.

Question 4

An IR spectrum of an unknown organic molecule having the formula C₃H₆O₂ reveals strong absorptions at 2500-3400 cm^-¹, 1715 cm^-¹, and 1230 cm^-¹.To what class of compounds does the unknown belong?

Accepted Answer

The strong absorptions at 2500-3400 cm^-1, 1715 cm^-1, and 1230 cm^-1 are characteristic of carboxylic acids. The broad absorption in the 2500-3400 cm^-1 range is due to O-H stretching, the 1715 cm^-1 absorption is indicative of the C=O stretching of a carboxylic acid, and the 1230 cm^-1 absorption can be associated with C-O stretching.

Question 5

As the wavelength of the radiation increases, the _______ decreases.

Accepted Answer

As the wavelength of radiation increases, the energy, frequency, and wave number all decrease. This is because energy and frequency are inversely proportional to wavelength, and wave number is directly proportional to frequency.

Question 6

An IR spectrum of an unknown organic molecule having the molecular formula of C₄H₈O shows no absorptions at 1630-1780 cm^-¹ or at 3200-3500 cm^-¹.To what class of compounds does the unknown belong?

Accepted Answer

The absence of absorptions at 1630-1780 cm^-1 rules out carbonyl-containing compounds (ketones, aldehydes, and carboxylic acids), and the lack of absorptions at 3200-3500 cm^-1 suggests the absence of O-H bonds, ruling out alcohols. This leaves ethers as the correct class, which do not exhibit these specific IR absorptions.

Question 7

How many peak(s) would you expect to see in the ¹H NMR spectrum of 1-bromobutane?

Accepted Answer

1-bromobutane has four different types of hydrogen environments, leading to four distinct peaks in its ¹H NMR spectrum.

Question 8

As the wavelength of the radiation decreases, the increases.

Accepted Answer

As the wavelength decreases, the energy, frequency, and wave number all increase according to the relationships in physics: energy is inversely proportional to wavelength, frequency is inversely proportional to wavelength, and wave number is directly proportional to the inverse of wavelength.

Question 9

An IR spectrum of an unknown organic molecule having the formula C₃H₆O reveals a strong absorption at 1230 cm^-¹ and has no absorption over 3000 cm^-¹.To what class of compounds does the unknown belong?

Accepted Answer

The strong absorption at 1230 cm^-1 is indicative of an ether (C-O-C stretch), and the lack of absorption over 3000 cm^-1 suggests the absence of O-H or N-H bonds, which rules out alcohols and amines. Aldehydes and alkynes do not show this specific absorption pattern.

Question 10

Which of the following forms of electromagnetic radiation has the highest energy?

Accepted Answer

X-rays have the highest energy among the options listed, as the energy of electromagnetic radiation increases with higher frequencies and shorter wavelengths, and x-rays have shorter wavelengths than ultraviolet (UV), visible light, infrared, and radio waves.

Question 11

Which of the following compounds will not have a broad band in the 3000 to 3600 cm^-¹ region of its IR spectrum?

Accepted Answer

The answer of Which of the following compounds will not...

Question 12

How many peaks would you expect to see in the ¹H NMR spectrum for the following compound:

Accepted Answer

The answer of How many peaks would you expect to...

Question 13

Which bond would show a strong, broad absorption in the IR between 3600 and 3200 cm^-¹?

Accepted Answer

The O-H bond shows a strong, broad absorption in the IR spectrum between 3600 and 3200 cm^-1 due to the stretching vibrations of the hydrogen bonded to oxygen, which is characteristic of alcohols and carboxylic acids.

Question 14

Which of the following forms of electromagnetic radiation has the longest wavelength?

Accepted Answer

Radiowaves have the longest wavelength among the options listed, with wavelengths ranging from about one millimeter to 100 kilometers or more.

Question 15

Which bond would show a strong, sharp absorption in the IR between 1200 and 1000 cm^-¹?

Accepted Answer

C-O bonds typically show a strong, sharp absorption in the IR spectrum between 1200 and 1000 cm^-1, which is characteristic of their stretching vibrations.

Question 16

Which bond would show a strong, sharp absorption in the IR between 1800 and 1700 cm^-¹?

Accepted Answer

The C=O bond typically shows a strong, sharp absorption in the IR spectrum between 1800 and 1700 cm^-1 due to its stretching vibration.

Question 17

An IR spectrum of an unknown organic molecule having the formula C₃H₆O reveals a strong absorption at 1725 cm^-¹.To what class of compounds does the unknown belong?

Accepted Answer

A strong absorption at 1725 cm^-1 is characteristic of the carbonyl stretch in ketones.

Question 18

An IR spectrum of an unknown organic molecule having the formula C₂H₄O reveals a strong absorption at 1715-1725 cm^-¹.To what class of compounds does the unknown belong?

Accepted Answer

The strong absorption at 1715-1725 cm^-1 is characteristic of the C=O stretching vibration found in aldehydes.

Question 19

In the ¹H NMR spectrum of the following molecule, the protons on which carbon will have the most downfield chemical shift?

Accepted Answer

The answer of In the ¹H NMR spectrum of the...

Question 20

The IR spectrum stretching frequency that has the highest energy occurs for which of these bonds?

Accepted Answer

The O-H bond has the highest energy stretching frequency because oxygen is more electronegative than carbon, chlorine, or hydrogen. This means that the oxygen atom pulls the electrons in the O-H bond more strongly than the other atoms, which results in a stronger bond and a higher stretching frequency.

Quiz 12: Spectroscopy and Structure Determination

Bending vibrations in the infared region occur at:

The area in the infared spectrum between 1400 and 400 cm-1 is called the .

Which bond would show a sharp absorption in the IR between 3000 and 2800 cm-1?

An IR spectrum of an unknown organic molecule having the formula C3H6O2 reveals strong absorptions at 2500-3400 cm-1, 1715 cm-1, and 1230 cm-1.To what class of compounds does the unknown belong?

As the wavelength of the radiation increases, the _______ decreases.

An IR spectrum of an unknown organic molecule having the molecular formula of C4H8O shows no absorptions at 1630-1780 cm-1 or at 3200-3500 cm-1.To what class of compounds does the unknown belong?

How many peak(s) would you expect to see in the 1H NMR spectrum of 1-bromobutane?

As the wavelength of the radiation decreases, the increases.

An IR spectrum of an unknown organic molecule having the formula C3H6O reveals a strong absorption at 1230 cm-1 and has no absorption over 3000 cm-1.To what class of compounds does the unknown belong?

Which of the following forms of electromagnetic radiation has the highest energy?

Which of the following compounds will not have a broad band in the 3000 to 3600 cm-1 region of its IR spectrum?

How many peaks would you expect to see in the 1H NMR spectrum for the following compound:

Which bond would show a strong, broad absorption in the IR between 3600 and 3200 cm-1?