Topic 19

Question 1

What are the types of radiation and their molecular effects?

Answer 1

Infrared: Causes bonds to vibrate; identifies bond types.
Microwaves: Causes molecules to rotate (used in heating).
Radio Waves: Alters hydrogen nucleus spin states (NMR spectroscopy).
Ultraviolet: Breaks bonds (e.g., Cl-Cl, C-Cl).

Question 2

What is the principle of Nuclear Magnetic Resonance (NMR)?

Answer 2

Uses radiowaves to analyze hydrogen arrangements.

Proton NMR Signals: One per set of equivalent hydrogens.

Question 3

How is the intensity of NMR signals determined?

Answer 3

Proportional to number of equivalent hydrogens.

Question 4

What type of solvents are used in NMR?

Answer 4

Must lack ¹H atoms (e.g., CDCl₃, CCl₄).

Question 5

What is used for calibration in NMR?

Answer 5

TMS (tetramethylsilane) used as a reference.

Question 6

How are chemical shifts in NMR measured?

Answer 6

Measured in ppm.

Question 7

What factors affect chemical shifts in NMR?

Answer 7

Electronegativity of neighboring atoms/groups increases the shift.

Question 8

What is the (n+1) rule in NMR?

Answer 8

Splitting Patterns: (n+1) rule, where n = number of neighboring H atoms.

Question 9

What does the molecular ion peak in mass spectrometry represent?

Answer 9

Highest m/z ratio corresponds to molecular mass (Mr).

Question 10

What causes fragmentation peaks in mass spectrometry?

Answer 10

Peaks due to fragments of the molecular ion.

Question 11

What are the uses of mass spectrometry?

Answer 11

Determines molecular structure and functional groups.

Question 12

What is the principle of Infrared (IR) Spectroscopy?

Answer 12

Bonds absorb IR at characteristic wavenumbers, causing vibration.

Question 13

How are functional groups identified in IR spectroscopy?

Answer 13

Above 1500 cm⁻¹.

Question 14

What is the wavenumber range for C=O in IR spectroscopy?

Answer 14

1640-1750 cm⁻¹.

Question 15

What is the wavenumber range for O-H (acid) in IR spectroscopy?

Answer 15

2500-3300 cm⁻¹ (broad).

Question 16

What is the wavenumber range for O-H (alcohol) in IR spectroscopy?

Answer 16

3200-3550 cm⁻¹.

Question 17

What is the fingerprint region in IR spectroscopy?

Answer 17

Below 1500 cm⁻¹, unique to each compound.

Question 18

What is the principle of chromatography?

Answer 18

Separates mixture components based on phase interaction.

Question 19

What are the phases in chromatography?

Answer 19

Mobile Phase: Liquid or gas.
Stationary Phase: Solid or liquid on solid support.

Question 20

What are the techniques used in chromatography?

Answer 20

TLC: Separates compounds; calculate Rf values.
Gas Chromatography (GC): Separates volatile liquids; uses retention time.
HPLC: Mobile phase is liquid; stationary phase is silica.

Question 21

What is GC-MS?

Answer 21

Combines gas chromatography with mass spectrometry for precise component identification.

Question 22

What are the applications of GC-MS?

Answer 22

Forensics, environmental analysis, security.

Question 23

What are the steps to identify a compound?

Answer 23

1. Elemental Analysis: Calculate empirical formula.
2. Mass Spectrometry: Use molecular ion peak for molecular formula.
3. IR Spectra: Identify functional groups.
4. NMR Spectra: Determine hydrogen environments and chain structure.