infra red

What are the main strengths of NMR?

Provides detailed structural information and can identify the arrangement of atoms within a molecule.

What are the main limitations of NMR?

Requires relatively pure samples, larger sample quantities, and expensive equipment.

When is NMR the preferred technique?

When detailed structural elucidation is required.

What information does ¹H NMR provide?

Information about hydrogen environments within a molecule.

What information does ¹³C NMR provide?

Information about carbon environments within a molecule.

Which technique provides the most detailed structural information?

NMR spectroscopy.

What are the main components of an IR spectrometer?

IR source, sample holder, detector, and computer.

How is an IR spectrum generated?

Molecules absorb specific IR frequencies causing vibrations, producing characteristic absorption peaks.

What information does IR spectroscopy provide?

Identification of functional groups present in a molecule.

What are the strengths of IR spectroscopy?

Fast, inexpensive, and useful for functional group identification.

What are the limitations of IR spectroscopy?

Provides limited structural information.

When is IR the preferred technique?

For rapid identification of functional groups.

Which technique is the fastest and cheapest for identifying functional groups?

IR spectroscopy.

Where is the O-H stretch found in IR spectroscopy?

Broad peak at 3200-3600 cm⁻¹.

Where is the N-H stretch found in IR spectroscopy?

Broad peak at 3300-3500 cm⁻¹.

Where is the C-H stretch found in IR spectroscopy?

Around 2850-3100 cm⁻¹.

Where is the C=O stretch found in IR spectroscopy?

Strong sharp peak at 1650-1750 cm⁻¹.

What is the fingerprint region?

The region below 1500 cm⁻¹ that is unique to each compound.

How does an O-H peak differ from a C=O peak?

O-H peaks are broad whereas C=O peaks are sharp and intense.

What does mass spectrometry measure?

The mass-to-charge ratio (m/z) of ions.

What are the main stages of mass spectrometry?

Ionisation, mass analysis, and detection.

What is the pathway through a mass spectrometer?

Sample → Ion source → Mass analyser → Detector.

What is the molecular ion peak?

The peak corresponding to the intact ionised molecule.

What is the base peak?

The most intense peak in a mass spectrum.

What is electron ionisation (EI)?

A hard ionisation technique that causes extensive fragmentation.

What is electrospray ionisation (ESI)?

A soft ionisation technique that causes minimal fragmentation.

Why can the same compound give different mass spectra?

Different ionisation methods produce different fragmentation patterns.

What is fragmentation?

The breakdown of ions into smaller ions that provide structural information.

How does a Time-of-Flight analyser work?

Ions are separated according to the time taken to reach the detector.

How does a quadrupole analyser work?

Electric fields allow only selected m/z values to pass.

What isotope pattern indicates chlorine?

M and M+2 peaks in a 3:1 ratio.

What isotope pattern indicates bromine?

M and M+2 peaks in a 1:1 ratio.

What isotope pattern indicates two bromine atoms?

M, M+2 and M+4 peaks in a 1:2:1 ratio.

What isotope peak is characteristic of sulfur?

A small M+2 peak due to ³⁴S.

What is high-resolution mass spectrometry (HRMS)?

A technique that measures exact masses to determine molecular formulae.

What is tandem mass spectrometry (MS/MS)?

A technique where selected ions are fragmented and analysed again.

Why is MS/MS useful?

It provides additional structural information and improves compound identification.

What are the strengths of mass spectrometry?

High sensitivity, low sample requirement, and molecular mass determination.

What are the limitations of mass spectrometry?

Some compounds ionise poorly and spectra can be complex to interpret.

When is MS the preferred technique?

When molecular mass, molecular formula, or trace analysis is required.

Which analytical technique requires the smallest sample amount?

Mass spectrometry.

Which technique would you choose to identify an unknown functional group?

IR spectroscopy.

Which technique would you choose to determine an exact molecular formula?

High-resolution mass spectrometry.

Which technique would you choose to determine the complete structure of an unknown organic molecule?

NMR spectroscopy.

Which technique is best for identifying functional groups?

IR spectroscopy.

Which technique is best for determining molecular mass and formula?

Mass spectrometry.