CHEM 238 Exam 1 Questions with Verified Answers Latest Version 2025 Graded A+
Stretches > 3000 cm-1 - Answers Unsaturated, sp2 C-H stretches (double bonds)
Stretches < 3000 cm-1 - Answers saturated, sp3 C-H stretches (single bonds)
Both above/below 3000 cm-1 - Answers sp2 and sp3 C-H stretches (could be aromatic)
Overtone bands - Answers Small, round peaks around 1900-2000 cm-1, aromatic compounds
1700 cm-1 - Answers C=O carbonyl stretch (ketones, aldehydes, esters, etc.) The range is 1650-1750 cm-
1.
Alcohol O-H stretch - Answers Smooth and broad at 3400 cm-1
Carboxylic acid O-H stretch - Answers EXTREMELY broad with rough edges at 3400 cm-1. Way larger
than the alcohol stretch
Mass Spectroscopy - Answers Blasting a molecule into pieces, and then determining the molecule's
structure based off of the pieces' mass. First, knock an electron out of the molecule (bonding or
nonbonding). This is now the molecular ion. The molecular ion has the same mass as the original, but a
charge of +1. In order to detect a particle, it must be charged. Then, the molecular ion will undergo
fragmentation by breaking a single covalent bond.
Common hydrocarbon spectroscopy peaks - Answers Methyl - 15
Ethyl - 29
Propyl - 43
Butyl - 57
Conjugated double bonds - Answers Alternating double/single bonds (more stable)
Non-conjugated double bonds - Answers NOT alternating double bonds (less stable)
Cumulated double bonds - Answers A carbon attached to 2 double bonds H-C=C=C-H
Allylic carbocation - Answers A carbon with a positive charge, one carbon away from a C=C double bond
1, 2 product (conjugated dienes) - Answers -kinetic product
-less stable, but formed more quickly
-favored at low temperatures
-lower activation energy
-cannot go in reverse (not enough energy)
Stretches > 3000 cm-1 - Answers Unsaturated, sp2 C-H stretches (double bonds)
Stretches < 3000 cm-1 - Answers saturated, sp3 C-H stretches (single bonds)
Both above/below 3000 cm-1 - Answers sp2 and sp3 C-H stretches (could be aromatic)
Overtone bands - Answers Small, round peaks around 1900-2000 cm-1, aromatic compounds
1700 cm-1 - Answers C=O carbonyl stretch (ketones, aldehydes, esters, etc.) The range is 1650-1750 cm-
1.
Alcohol O-H stretch - Answers Smooth and broad at 3400 cm-1
Carboxylic acid O-H stretch - Answers EXTREMELY broad with rough edges at 3400 cm-1. Way larger
than the alcohol stretch
Mass Spectroscopy - Answers Blasting a molecule into pieces, and then determining the molecule's
structure based off of the pieces' mass. First, knock an electron out of the molecule (bonding or
nonbonding). This is now the molecular ion. The molecular ion has the same mass as the original, but a
charge of +1. In order to detect a particle, it must be charged. Then, the molecular ion will undergo
fragmentation by breaking a single covalent bond.
Common hydrocarbon spectroscopy peaks - Answers Methyl - 15
Ethyl - 29
Propyl - 43
Butyl - 57
Conjugated double bonds - Answers Alternating double/single bonds (more stable)
Non-conjugated double bonds - Answers NOT alternating double bonds (less stable)
Cumulated double bonds - Answers A carbon attached to 2 double bonds H-C=C=C-H
Allylic carbocation - Answers A carbon with a positive charge, one carbon away from a C=C double bond
1, 2 product (conjugated dienes) - Answers -kinetic product
-less stable, but formed more quickly
-favored at low temperatures
-lower activation energy
-cannot go in reverse (not enough energy)
