IR, NMR, and mass spectrometry interpretation concepts for determining organic molecule structure, tested on the MCAT.
40 cards · basic cards · AI-written, checked twice. Edit anything.
- What molecular motions does IR spectroscopy detect?
- Bond stretching and bending vibrations
- What is the characteristic IR range for an O-H stretch in alcohols?
- 3200-3550 cm-1, broad
- How does an amine N-H stretch differ in appearance from an alcohol O-H stretch in IR?
- N-H is sharper and less broad than O-H
- What is the typical IR range for a carbonyl (C=O) stretch?
- 1650-1750 cm-1, strong
- What is the typical IR range for sp3 C-H stretches in alkanes?
- 2850-2960 cm-1
- What is the characteristic IR range for a terminal alkyne C-H stretch?
- About 3300 cm-1, sharp
- What is the typical IR range for a C=C stretch in alkenes?
- 1620-1680 cm-1, weak to medium
- What is the typical IR range for a C triple bond C stretch in alkynes?
- 2100-2260 cm-1, weak
- What is the typical IR range for a nitrile C triple bond N stretch?
- 2200-2260 cm-1
- Why does a carboxylic acid O-H stretch look different from an alcohol O-H stretch in IR?
- It is much broader, spanning roughly 2500-3300 cm-1, due to strong hydrogen bonding
- How does an ester C=O stretch frequency compare to a ketone C=O stretch?
- Ester C=O appears at higher wavenumber, about 1735-1750 cm-1, than a ketone
- Why does an amide C=O stretch appear at lower wavenumber than a ketone?
- Resonance delocalization of the nitrogen lone pair lowers the C=O bond order
- What is the fingerprint region of an IR spectrum?
- The 1500-400 cm-1 region, unique to each molecule
- What two peaks near 2720 and 2820 cm-1 are diagnostic for an aldehyde in IR?
- A pair of weak C-H stretch bands from the aldehyde proton
- What molecular property must change during a vibration for it to produce an IR absorption?
- The dipole moment of the bond