NMR spectroscopy

Question 1

Four-Step Spectrum Interpretation

Answer 1

A systematic approach to interpreting NMR spectra: count signals, check integration, match chemical shifts, and analyze splitting patterns

Question 2

Superconducting Magnet

Answer 2

A powerful magnet (1–20 T) that houses the sample probe and is cooled by liquid He & N₂ to maintain superconductivity

Question 3

Nuclear Magnetic Resonance (NMR) Spectroscopy

Answer 3

A technique that detects atomic nuclei and their chemical environments within molecules using an applied magnetic field and radio-wave interactions

Question 4

Deuterated Solvent

Answer 4

A solvent in which the hydrogen atoms are replaced with deuterium, used to dissolve samples for NMR analysis without interfering with the spectrum

Question 5

Deshielding

Answer 5

The increase of the external magnetic field experienced by a nucleus due to the withdrawal of electrons, resulting in a larger chemical shift

Question 6

¹³C NMR

Answer 6

A type of NMR spectroscopy that detects ¹³C nuclei, typically run with proton decoupling to produce singlet signals for each non-equivalent carbon

Question 7

Integration

Answer 7

A measure of the relative number of equivalent protons in different environments, used to determine proton ratios

Question 8

Shielding

Answer 8

The reduction of the external magnetic field experienced by a nucleus due to the presence of surrounding electrons

Question 9

Chemical Shift Calculation

Answer 9

δ= sample frequency−TMS frequency / spectrometer operating frequency ×10^6 ppm

Question 10

Multiplicity

Answer 10

The splitting pattern of a signal due to the presence of adjacent protons, following the n+1 rule

Question 11

NMR-Active Isotopes

Answer 11

Isotopes that possess spin ½, such as ¹H and ¹³C, which can be detected using NMR spectroscopy

Question 12

Chemical Shift

Answer 12

A measure of the shielding or deshielding of nuclei by local magnetic fields created by electrons, expressed in ppm relative to TMS

Question 13

Resonance

Answer 13

The absorption of radio-frequency energy that flips the spin state of NMR-active nuclei in a strong magnetic field

Question 14

Equivalent Protons

Answer 14

Protons that have the same chemical environment and therefore produce a single signal in the NMR spectrum

Question 15

TMS (Tetramethylsilane)

Answer 15

An internal reference compound added to NMR samples, with a chemical shift of 0 ppm

Question 16

n+1 Rule

Answer 16

A rule that states the multiplicity of a signal is equal to the number of adjacent protons plus one

Question 17

Magnetic Resonance Imaging (MRI)

Answer 17

An application of ¹H NMR that images tissue water in the body, using variations in T₂ relaxation times to distinguish normal and pathological regions

Question 18

What property makes a nucleus NMR-active?

Answer 18

It must have a non-zero nuclear spin (e.g., ¹H, ¹³C)

Question 19

Why is a strong magnet required for NMR?

Answer 19

The energy difference between spin states is extremely small.

Question 20

When do protons give the same signal?

Answer 20

When they are chemically equivalent (same environment)

Question 21

Step 1 of interpreting a spectrum?

Answer 21

Count the number of signals (number of environments).

Question 22

step 2 of interpreting a spectrum?

Answer 22

Examine integration ratios.

Question 23

step 3 of interpreting a spectrum?

Answer 23

Assess chemical shift regions for functional groups.

Question 24

step 4 of interpreting a spectrum?

Answer 24

Inspect splitting patterns to determine connectivity.