CHEM10050 : Guiry Lecture 22 - Infrared Spectroscopy

What is infrared spectroscopy used for?

a) Identification of functional groups

b) Measuring protein structures

c) Detecting DNA mutations

d) Determining cell viability

a) Identification of functional groups

What is infrared radiation absorbed and converted into during IR spectroscopy?

a) Energy of molecular rotation

b) Energy of electronic excitation

c) Energy of molecular vibration

d) Energy of nuclear spin

c) Energy of molecular vibration

What range of wavelengths is most useful for organic molecules in IR spectroscopy?

a) 0.01-0.1 μm

b) 2.5-16 μm

c) 20-200 μm

d) 500-1000 μm

b) 2.5-16 μm

What unit is used to express the position of an IR band?

a) Meters

b) Microns

c) Hertz

d) Wavenumbers

d) Wavenumbers

What is the relationship between frequency and wavelength in IR spectroscopy?

a) Frequency is inversely proportional to wavelength

b) Frequency is directly proportional to wavelength

c) Frequency and wavelength are not related in IR spectroscopy

d) Frequency and wavelength have an inverse square relationship in IR spectroscopy

a) Frequency is inversely proportional to wavelength

What unit is used in IR spectroscopy to directly correspond to energy?

a) Hertz

b) Microns

c) Wavenumbers

d) Meters

c) Wavenumbers

What factors affect the position of an IR band?

a) Bond strength and masses of the bonded atoms

b) Temperature and pressure

c) pH and ionic strength

d) Solvent polarity and concentration

a) Bond strength and masses of the bonded atoms

What type of spectroscopy is IR spectroscopy?

a) Absorption spectroscopy

b) Emission spectroscopy

c) Fluorescence spectroscopy

d) NMR spectroscopy

a) Absorption spectroscopy

What is the range of wavenumbers typically used in IR spectroscopy?

a) 10-100 cm-1

b) 100-1000 cm-1

c) 1000-10,000 cm-1

d) 10,000-100,000 cm-1

c) 1000-10,000 cm-1

How does energy absorption occur in IR spectroscopy?

a) Energy is absorbed only when it corresponds exactly to DE

b) Energy is absorbed randomly throughout the spectrum

c) Energy is absorbed in a continuous manner without any restrictions

d) Energy is not absorbed in IR spectroscopy

a) Energy is absorbed only when it corresponds exactly to DE

What is the primary use of infrared spectroscopy?

a) Identification of functional groups

b) Determination of bond angles

c) Measurement of molecular weight

d) Detection of radioactivity

a) Identification of functional groups

What range of wavelengths is most useful for organic molecules in infrared spectroscopy?

a) 2-5 μm

b) 5-10 μm

c) 10-15 μm

d) 15-20 μm

c) 10-15 μm

What unit is used to express the position of an IR band?

a) Joules

b) Hertz

c) Wavenumbers

d) Nanometers

c) Wavenumbers

What does v represent in IR spectroscopy?

a) Vibrational frequency

b) Wavelength

c) Energy

d) Mass

a) Vibrational frequency

What is the force constant of a bond?

a) The strength of the bond

b) The energy required to break the bond

c) The mass of the atoms in the bond

d) The frequency of the bond vibration

a) The strength of the bond

What is the reduced mass of a diatomic molecule?

a) (m1m2)

b) (m1+m2)

c) (m1/m2)

d) (m2/m1)

b) (m1+m2)

Which bond has the highest vibrational frequency?

a) C≡C

b) C=C

c) C-C

d) They all have the same vibrational frequency

a) C≡C

Which bond vibrates at the lowest wavenumber?

a) C-H

b) C-C

c) C-O

d) C-I

d) C-I

What type of motion occurs at lower energy than the typical stretching motion in IR spectroscopy?

a) Rotational motion

b) Vibrational motion

c) Bending motion

d) Translational motion

c) Bending motion

What is the typical wavenumber for C-H stretching motion?

a) 500 cm^-1

b) 1100 cm^-1

c) 1200 cm^-1

d) 3000 cm^-1

d) 3000 cm^-1

What is the purpose of using IR spectroscopy generally?

a) To confirm functional group conversion in a reaction

b) To identify the structure of unknown compounds

c) To measure the pH of a solution

a) To confirm functional group conversion in a reaction

What type of reaction is used to convert a carboxylic acid to an alcohol using LiAIH4?

a) Ester formation

b) Ketone reduction

c) Acid reduction

c) Acid reduction

What is the range of wavenumbers that is most useful for organic molecules in IR spectroscopy?

a) 10-50 μm

b) 2.5-16 μm

c) 1-5 μm

b) 2.5-16 μm

Which of the following bonds would have the highest stretching frequency?

a) C=C

b) C-C

c) C≡C

c) C≡C

Which of the following functional groups would have the highest stretching frequency?

a) C-Cl

b) C-O

c) C-I

c) C-I

Which type of motion occurs at lower energy (lower v) than the typical stretching motion?

a) Bending

b) Twisting

c) Vibrating

a) Bending

Which of the following is not a product of amide hydrolysis?

a) Ammonia

b) Carboxylic acid

c) Alcohol

c) Alcohol

Which reagent is used to oxidize alcohols to ketones in IR spectroscopy?

a) NaBH4

b) K2Cr2O7

c) LiAIH4

b) K2Cr2O7

What does the value of the force constant (k) indicate about a bond in IR spectroscopy?

a) How much energy it takes to stretch the bond

b) The frequency of the bond stretching motion

c) The mass of the bonded atoms

a) How much energy it takes to stretch the bond

What is the purpose of measuring wavenumbers in IR spectroscopy?

a) To identify the type of bond present

b) To calculate the force constant of the bond

c) To determine the energy of the bond stretching motion

c) To determine the energy of the bond stretching motion