M6L10b - MPQ - Amino Acids.pptx

Infrared spectroscopy works by:

• measuring the absorption of infrared light by molecules

• measuring the emission of visible light by atoms

• detecting the reflection of ultraviolet light by surfaces

• analyzing the scattering of X-rays by crystals

The area of the spectrum that should not be used when identifying functional groups is:

• the fingerprint region

• the functional group region

• the visible region

• the ultraviolet region

Distinguish between a carboxylic acid and aldehyde/ketone on an IR spectrum.

• Carboxylic acids show a broad O-H stretch around 2500-3300 cm⁻¹, which is absent in aldehydes/ketones.

• Aldehydes show a sharp N-H stretch around 3300 cm⁻¹, which is absent in carboxylic acids.

• Ketones show a broad O-H stretch around 2500-3300 cm⁻¹, which is absent in carboxylic acids.

• Carboxylic acids and aldehydes/ketones have identical IR spectra.

A peak at 2850-3100 cm⁻¹ on an IR spectrum represents:

• C-H stretching

• O-H stretching

• C=O stretching

• N-H bending

Butan-1-ol was oxidised using acidified potassium dichromate. The organic product was analysed by infra-red spectroscopy. The infra-red spectrum obtained is shown below. What is the organic product identified from the spectrum?

• Butanoic acid

• Butanal

• Butanone

• Butene

What does the absorption of infrared radiation cause in covalent bonds, and how does this relate to the production of a spectrum?

• Absorption of infrared radiation causes covalent bonds to vibrate; different bonds absorb different wavelengths producing a spectrum.

• Absorption of infrared radiation causes covalent bonds to break apart, releasing visible light and producing a spectrum.

• Absorption of infrared radiation causes covalent bonds to become rigid, preventing any absorption and thus no spectrum is produced.

• Absorption of infrared radiation causes covalent bonds to rotate freely, which results in the emission of ultraviolet light and a spectrum.

What is the fingerprint region in infrared spectroscopy?

• Fingerprint region or 0-1500cm⁻¹

• Functional group region or 4000-2500cm⁻¹

• Visible region or 15000-4000cm⁻¹

• Ultraviolet region or 200-400nm

Which functional group has both C=O and O-H absorption, and which has only C=O absorption: carboxylic acid or aldehyde/ketone?

• Carboxylic has both C=O and O-H absorption; aldehyde/ketone only C=O

• Aldehyde/ketone has both C=O and O-H absorption; carboxylic only C=O

• Both carboxylic acid and aldehyde/ketone have only C=O absorption

• Both carboxylic acid and aldehyde/ketone have both C=O and O-H absorption

Which type of bonds are indicated by C-H in infrared spectroscopy?

• C-H bonds

• O-H bonds

• N-H bonds

• C=O bonds

In the IR spectrum of butanoic acid, what does the peak at ~1700cm⁻¹ correspond to?

• C=O

• O-H

• C-H

• C-O