IR Spectroscopy and NMR Spectroscopy

Question 1

What is the importance of structural elucidation in organic compounds?

Answer 1

Structural elucidation is important for understanding the molecular structure and properties of organic compounds.

Question 2

What techniques does the Canadian Food Inspection Agency (CFIA) use to investigate food safety?

Answer 2

CFIA uses spectroscopic techniques, including infrared spectroscopy, to investigate the safety and quality of food.

Question 3

What does infrared spectroscopy collect from food products?

Answer 3

Infrared spectroscopy collects a unique ‘fingerprint’ spectrum from food products.

Question 4

What does the degree of unsaturation (DOU) indicate in a molecule?

Answer 4

DOU indicates the number of π bonds and/or rings in a molecule.

Question 5

How is the degree of unsaturation calculated?

Answer 5

DOU = (2C + 2) – (# of H) + Group V – Group VII.

Question 6

What happens to the hydrogen count in a molecule with a double bond?

Answer 6

Each double bond results in a loss of 2 H from the formula CnH2n+2.

Question 7

What information does Mass Spectrometry (MS) provide?

Answer 7

MS provides information about the mass of a compound and its fragments.

Question 8

What is the significance of the molecular ion peak in a mass spectrum?

Answer 8

The molecular ion peak (M+) represents the molecular mass of the compound.

Question 9

What does spectroscopy measure?

Answer 9

Spectroscopy measures the interaction between a molecule and electromagnetic radiation.

Question 10

What types of vibrations does infrared radiation cause in molecules?

Answer 10

Infrared radiation causes stretching and bending vibrations of bonds that contain a dipole.

Question 11

What is the typical range for the O-H stretching in alcohols as seen in IR spectroscopy?

Answer 11

O-H stretching in alcohols occurs at 3200 – 3600 cm-1.

Question 12

What are the typical wavenumbers for C=O bands in carbonyl compounds?

Answer 12

C=O bands appear between 1670 - 1780 cm-1.

Question 13

How does Nuclear Magnetic Resonance (NMR) spectroscopy work?

Answer 13

NMR works by aligning magnetic moments of nuclei in an external magnetic field and detecting emitted signals during relaxation.

Question 14

What does a 1H NMR spectrum provide information about?

Answer 14

A 1H NMR spectrum provides information about hydrogen types, the number of signals, integration, and chemical shifts.

Question 15

What does the position on the x-axis of each signal in an NMR spectrum indicate?

Answer 15

The position indicates the chemical environment of each proton type.

Question 16

What is the difference between NMR and MRI?

Answer 16

NMR is used for chemical analysis, while MRI is a non-invasive imaging technique for medical diagnosis.

Question 17

True or False: Bonds without a dipole give bands in infrared spectroscopy.

Answer 17

False

Question 18

Fill in the blank: The degree of unsaturation is the number of ______ bonds and/or rings in a molecule.

Answer 18

[π]

Question 19

What are chlorofluorocarbons (CFCs) known for?

Answer 19

CFCs are known for their role in ozone depletion and as potent greenhouse gases.

Question 20

What is the range of magnetic field strength for small organic molecules in NMR?

Answer 20

300-700 MHz

Question 21

What does integration in a 1H NMR spectrum indicate?

Answer 21

Integration indicates the relative number of protons associated with each signal.

Question 22

What is the significance of the fingerprint region in IR spectroscopy?

Answer 22

The fingerprint region is less useful for identifying functional groups.

Question 23

What is the impact of structural changes in organic compounds?

Answer 23

Small structural changes can cause dramatic changes in properties, including physiological effects.

Question 24

What does the term ‘chemical shift’ refer to in NMR spectroscopy?

Answer 24

Chemical shift refers to the position of each signal on the x-axis, indicating the unique chemical environment of protons.

Question 25

What does the number of signals in a 1H NMR spectrum indicate?

Answer 25

The number of hydrogen types present in the molecule. ## Footnote Each signal corresponds to a hydrogen or group of hydrogens in a different chemical environment.

Question 26

What does the integration in a 1H NMR spectrum represent?

Answer 26

The peak area for each hydrogen type, proportional to the number of hydrogen atoms it represents. ## Footnote Integration is shown as a ratio in the spectrum.

Question 27

What does the chemical shift indicate in a 1H NMR spectrum?

Answer 27

The position on the x-axis of each signal, reflecting the chemical environment of each proton type. ## Footnote It includes factors like hybridization of attached carbons and the presence of adjacent functional groups.

Question 28

What are chemically equivalent hydrogens?

Answer 28

Hydrogens that have identical environments and identical chemical shifts. ## Footnote They can be interchanged by bond rotation or symmetry.

Question 29

How many hydrogen types would you expect in a mono-substituted aromatic ring?

Answer 29

4 hydrogen types. ## Footnote The integration corresponds to 5 H.

Question 30

What is the typical range of chemical shifts for aromatic protons?

Answer 30

6.5 – 8.5 ppm. ## Footnote Peaks from aromatic protons can overlap within this range.

Question 31

What does shielding in NMR refer to?

Answer 31

The reduction of the apparent magnetic field at a nucleus due to surrounding electrons. ## Footnote Shielded nuclei have signals upfield (lower chemical shift).

Question 32

What effect do electronegative atoms have on chemical shifts?

Answer 32

They deshield protons, causing shifts to higher ppm (downfield). ## Footnote The effect is additive and diminishes with distance.

Question 33

What is magnetic anisotropy in NMR?

Answer 33

The effect where pi-electrons generate a local current that affects the magnetic environment of nearby nuclei. ## Footnote This can lead to deshielding or shielding based on the position relative to the π-system.

Question 34

What is the chemical shift range for aldehyde protons?

Answer 34

9.0 – 10.0 ppm.

Question 35

What is the chemical shift range for alcohol and amine protons?

Answer 35

1 – 5 ppm (broad) and 8-10 ppm (broad).

Question 36

What is the chemical shift range for carboxylic acid protons?

Answer 36

10 – 13 ppm (broad).

Question 37

Fill in the blank: The chemical shift (δ) of a proton is calculated as _______.

Answer 37

[νsample (Hz from TMS) / νspectrometer (MHz)].

Question 38

True or False: The integration of a signal in a 1H NMR spectrum is directly proportional to the number of different hydrogen types.

Answer 38

False. ## Footnote Integration is proportional to the number of hydrogen atoms represented by the signal, not the types.

Question 39

What happens to signals from hydrogen atoms on heteroatoms due to H-bonding?

Answer 39

They usually appear as broad signals with variable chemical shifts.

Question 40

What is the chemical shift range for alkynyl protons?

Answer 40

2.0 – 3.0 ppm.

Question 41

What does the term 'chemical environment' refer to in NMR spectroscopy?

Answer 41

The local electronic environment surrounding a proton that affects its resonance frequency.

Question 42

What type of signal do protons in a π-system typically produce in NMR?

Answer 42

A deshielded signal that appears downfield compared to alkane protons.