Question 1

Which of the following structures is consistent with a compound that displays a molecular ion peak at 56 and infrared signals at 2250 and 3600-3200 cm^-1? A)I B)II C)III D)IV

Accepted Answer

B

Question 2

-Which of the following statements is (are)true about the IR spectrum of the compound drawn below? A)It shows absorptions at 3000-3150 cm^-1 and 1720 cm^-1. B)It shows absorptions at 3000-2850 cm^-1 and 2150 cm^-1. C)It shows absorptions at 2250 cm^-1 and 1650 cm^-1. D)It shows absorptions at 2250 cm^-1 and 1720 cm^-1. E)Both statements (It shows absorptions at 3000-2850 cm^-1 and 2250 cm^-1)and (It shows absorptions at 2250 cm^-1 and 1720 cm^-1)are true.

Accepted Answer

E

Question 3

Consider the three organic compounds drawn below.Which of the following statements is (are)true about the IR spectra of I,II,and III? A)I shows strong absorptions at 2950 cm^-1 and 1700 cm^-1. B)II shows strong absorptions at 2950 cm^-1 and 2250 cm^-1. C)III shows strong absorptions at 2950 cm^-1 and 3200-3600 cm^-1. D)Statements (I shows strong absorptions at 2950 cm^-1 and 1700 cm^-1)and (III shows strong absorptions at 2950 cm^-1 and 3200-3600 cm^-1)are true.

Accepted Answer

I shows strong absorptions at 2950 cm^-1 (C-H stretching in alkanes) and 1700 cm^-1 (C=O stretching in ketones and aldehydes).

II contains a triple bond as well as C-H bonds so it should show strong absorptions at both 2950 cm^-1 and 2250 cm^-1 (C≡C stretching in alkynes).

III contains an -OH group so it should show a broad absorption in the region of 3200-3600 cm^-1 (O-H stretching in alcohols) as well as C-H stretching at 2950 cm^-1.

Therefore, statements (I and III) are true.

Question 4

Which of the indicated C-H bonds absorbs at the lowest wave number in the IR spectrum? 
A)I
B)II
C)III
D)IV

Accepted Answer

The C-H bond in III absorbs at the lowest wave number in the IR spectrum because it is a sp hybridized C-H bond which has the highest s-character (50%) and therefore the highest bond strength. The stronger a bond, the lower the wave number at which it absorbs in the IR spectrum.

Question 5

Which of the following statement(s)is (are)true about a compound that has a molecular ion peak in its mass spectrum at mass 69 and shows a prominent peak in its IR spectrum at 2250 cm^-1? A)The compound has a molecular mass of 70. B)The compound contains a C=O group. C)The compound contains a cyano or alkyne group. D)Both (The compound has a molecular mass of 70)and (The compound contains a C=O group)are true statements. E)Both (The compound has a molecular mass of 70)and (The compound contains a cyano or alkyne group)are true statements.

Accepted Answer

EThe molecular ion peak at mass 69 indicates the molecular mass of the compound is 69, not 70, making statement A incorrect and thus D and E need to be evaluated on the second part of their statements. The IR spectrum peak at 2250 cm^-1 is characteristic of cyano (C≡N) groups or alkynes (C≡C), not C=O groups, which typically absorb around 1700 cm^-1. Therefore, statement C is correct, and since A is incorrect, E is the correct combination statement, indicating the compound has a molecular mass of 69 and contains a cyano or alkyne group.

Question 6

Which of the following statements is (are)true about a compound that has a molecular ion peak in its mass spectrum at mass 104 and shows prominent peaks in its IR spectrum at 3200-2850 cm^-1? A)The compound has a molecular mass of 104. B)The compound contains a C=O group and C_sp₃-H hybridized bonds. C)The compound contains an OH group and C_sp₃-H hybridized bonds. D)Both (The compound has a molecular mass of 104)and (The compound contains a C=O group and C_sp₃-H hybridized bonds)are true statements. E)Both (The compound has a molecular mass of 104)and (The compound contains an OH group and C_sp₃-H hybridized bonds)are true statements.

Accepted Answer

The answer of Which of the following statements is (are)true...

Question 7

The functional group region of an infrared spectrum is A)where the cations appear. B)greater than or equal to 1500 cm^-1. C)less than 1500 cm^-1. D)greater than or equal to 2500 cm^-1.

Accepted Answer

The functional group region of an infrared spectrum is typically considered to be greater than or equal to 1500 cm^-1. This region is where most of the characteristic absorptions of different functional groups (like OH, NH, CO, etc.) occur, allowing for the identification of various chemical functionalities in a molecule.

Question 8

Stronger bonds will be found where in the infrared spectrum?
A)Higher molecular weight
B)Lower molecular weight
C)Lower wavenumbers
D)Higher wavenumbers

Accepted Answer

Stronger bonds will absorb energy at higher wavenumbers in the infrared spectrum, indicating a shorter bond length and higher bond strength.

Question 9

An alkyne C-H bond absorbs at higher wave number than an alkene C-H bond.What does this tell you about the strength of these two bonds?
A)The alkene C-H bond is stronger.
B)The alkyne C-H bond is stronger.
C)The alkene C-C bond is stronger.
D)The alkyne C-C bond is stronger.

Accepted Answer

The absorption of a C-H bond occurs at a higher wave number when the bond is stronger. Therefore, since the alkyne C-H bond absorbs at a higher wave number than the alkene C-H bond, it is stronger.

Question 10

Which of the following structures is consistent with a compound that displays a molecular ion peak at 103 and infrared signals at 2250 and 1600 cm^-1? A)I B)II C)III D)IV

Accepted Answer

The answer of Which of the following structures is consistent...

Question 11

You are given a bottle of an organic liquid and told it must be either cyclohexane or 1-hexene.Which of the following statements is (are)true about these two compounds? A)The two compounds can be differentiated by their mass spectra because they will have molecular ion peaks at different m/z. B)1-Hexene will show an absorption at 1650 cm^-1 but cyclohexane will not. C)Both cyclohexane and 1-hexene will show C-H absorptions at about 2950 cm^-1. D)Statements (1-Hexene will show an absorption at 1650 cm^-1 but cyclohexane will not)and (Both cyclohexane and 1-hexene will show C-H absorptions at about 2950 cm^-1)are both true. E)Statements (The two compounds can be differentiated by their mass spectra because they will have molecular ions at different masses),(1-Hexene will show an absorption at 1650 cm^-1 but cyclohexane will not),and (Both cyclohexane and 1- hexene will show C-H absorptions at about 2950 cm^-1)are all true.

Accepted Answer

The answer of You are given a bottle of an...

Question 12

Which of the following statements is (are)accurate about the IR spectrum of compounds I,II,and III below? A)Compound I shows absorptions at 2950 and 1700 cm^-1. B)Compound II shows absorptions at 3200-3600 and 1650 cm^-1. C)Compound III shows absorptions at 3200-3600 and 2950 cm^-1. D)Both (Compound I shows absorptions at 2950 and 1700 cm^-1)and (Compound II shows absorptions at 3200-3600 and 1650 cm^-1)are true.

Accepted Answer

Compound I shows a strong absorption at around 2950 cm-1, which is characteristic of C-H stretching in alkanes. It also shows an absorption around 1700 cm-1, which is characteristic of the carbonyl group in ketones or aldehydes. Compound II shows a broad absorption in the range of 3200-3600 cm-1, which is indicative of O-H stretching in alcohols or carboxylic acids. It also shows an absorption around 1650 cm-1, which is characteristic of the carbonyl group in amides or esters. Compound III shows a broad absorption in the range of 3200-3600 cm-1, which is again indicative of O-H stretching in alcohols or carboxylic acids. It also shows an absorption around 2950 cm-1, which is characteristic of C-H stretching in alkanes. Therefore, both statement A and statement B are true, and the correct answer is D.

Question 13

Which of the following statements is (are)true about a compound that has a molecular ion peak in its mass spectrum at mass 94 and shows prominent peaks in its IR spectrum at 3600-3200 and 1600 cm^-1? A)The compound has a molecular mass of 94. B)The compound contains a C=O group and C_sp₃-H hybridized bonds. C)The compound contains an OH group and a benzene ring. D)Both (The compound has a molecular mass of 94)and (The compound contains a C=O group and C_sp₃-H hybridized bonds)are true statements. E)Both (The compound has a molecular mass of 94)and (The compound contains an OH group and a benzene ring)are true statements.

Accepted Answer

The answer of Which of the following statements is (are)true...

Question 14

Why is the infrared absorption for the stretching motion of internal alkynes rarely observed?
A)They do not form cations.
B)They are too strong.
C)Stretching in internal alkynes does not involve a change in dipole moment.
D)They do not have hydrogens.

Accepted Answer

The stretching motion in internal alkynes does not involve a change in dipole moment, which is necessary for infrared absorption.

Question 15

What type(s)of molecular motion is (are)observed using infrared spectroscopy?
A)Stretching and bending
B)Rotation and excitation
C)Spin flipping
D)Fragmentation

Accepted Answer

Infrared spectroscopy measures the vibrational mode of molecules, which includes stretching and bending of covalent bonds. Rotation, excitation, spin flipping, and fragmentation are not typically observed using infrared spectroscopy.

Question 16

A compound X shows a molecular ion peak at m/z 72 in its mass spectrum,and a strong peak at ~1715 cm^-1 in its IR spectrum.Which structures are possible for compound X? A)I B)II C)III D)I and II

Accepted Answer

The answer of A compound X shows a molecular ion...

Question 17

In an IR spectrum,which of the indicated C-H bonds exhibits a stretching absorption at the largest wave number? 
A)I
B)II
C)III
D)IV

Accepted Answer

The answer of In an IR spectrum,which of the indicated...

Question 18

Why does an alkyne carbon-carbon triple bond vibrate at a higher wavenumber than an alkene carbon-carbon double bond?
A)It is stronger.
B)It is weaker.
C)It has fewer hydrogens.
D)It makes a less stable cation.

Accepted Answer

A carbon-carbon triple bond in an alkyne is stronger than a carbon-carbon double bond in an alkene because it is composed of two pi bonds and one sigma bond. This increased bond strength leads to faster and more energetic vibrations, resulting in a higher wavenumber in the infrared spectrum.

Question 19

Compared to a C-H bond,a C-D bond will vibrate where in the infrared spectrum?
A)Higher molecular weight
B)Lower molecular weight
C)Lower wavenumbers
D)Higher wavenumbers

Accepted Answer

The wavenumber of a bond vibration in the infrared spectrum is directly proportional to the bond's strength. A C-D bond is stronger than a C-H bond due to the higher electronegativity difference between carbon and deuterium compared to carbon and hydrogen. Therefore, the C-D bond will vibrate at a lower wavenumber (frequency) in the infrared spectrum.

Question 20

Which of the following statements is (are)true about a compound that has molecular ion peaks in its mass spectrum at mass 170 and 172 and shows prominent peaks in its IR spectrum at 3150-3000 and 1600 cm^-1? A)The compound is not pure. B)The compound contains a halogen. C)The compound contains an OH group and C_sp₃-H hybridized bonds. D)Both (The compound is not pure)and (The compound contains a halogen)are true statements. E)Both (The compound is not pure)and (The compound contains an OH group and C_sp₃-H hybridized bonds)are true statements.

Accepted Answer

The presence of molecular ion peaks at mass 170 and 172 suggests the compound contains a halogen, specifically chlorine, due to the natural isotopic abundance of Cl-35 and Cl-37 causing the M and M+2 peaks. The IR spectrum peaks do not directly indicate purity or specific functional groups like OH in this context.

Quiz 31: Spectroscopy B: Infrared Spectroscopy

Which of the following structures is consistent with a compound that displays a molecular ion peak at 56 and infrared signals at 2250 and 3600-3200 cm^-1?

-Which of the following statements is (are) true about the IR spectrum of the compound drawn below?

Consider the three organic compounds drawn below.Which of the following statements is (are) true about the IR spectra of I,II,and III?

Which of the indicated C-H bonds absorbs at the lowest wave number in the IR spectrum?

Which of the following statement(s) is (are) true about a compound that has a molecular ion peak in its mass spectrum at mass 69 and shows a prominent peak in its IR spectrum at 2250 cm^-1?

Which of the following statements is (are) true about a compound that has a molecular ion peak in its mass spectrum at mass 104 and shows prominent peaks in its IR spectrum at 3200-2850 cm^-1?

The functional group region of an infrared spectrum is

Stronger bonds will be found where in the infrared spectrum?

An alkyne C-H bond absorbs at higher wave number than an alkene C-H bond.What does this tell you about the strength of these two bonds?

Which of the following structures is consistent with a compound that displays a molecular ion peak at 103 and infrared signals at 2250 and 1600 cm^-1?

You are given a bottle of an organic liquid and told it must be either cyclohexane or 1-hexene.Which of the following statements is (are) true about these two compounds?

Which of the following statements is (are) accurate about the IR spectrum of compounds I,II,and III below?

Which of the following statements is (are) true about a compound that has a molecular ion peak in its mass spectrum at mass 94 and shows prominent peaks in its IR spectrum at 3600-3200 and 1600 cm^-1?

Why is the infrared absorption for the stretching motion of internal alkynes rarely observed?

What type(s) of molecular motion is (are) observed using infrared spectroscopy?

A compound X shows a molecular ion peak at m/z 72 in its mass spectrum,and a strong peak at ~1715 cm^-1 in its IR spectrum.Which structures are possible for compound X?

In an IR spectrum,which of the indicated C-H bonds exhibits a stretching absorption at the largest wave number?

Why does an alkyne carbon-carbon triple bond vibrate at a higher wavenumber than an alkene carbon-carbon double bond?

Compared to a C-H bond,a C-D bond will vibrate where in the infrared spectrum?

Which of the following statements is (are) true about a compound that has molecular ion peaks in its mass spectrum at mass 170 and 172 and shows prominent peaks in its IR spectrum at 3150-3000 and 1600 cm^-1?