CHEM 14C flash cards
47 cards for Structure of Organic Molecules, laid out week by week and timed around your exams. Free on iPhone and the web.
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- FinalThu, Mar 18, 2027A sample date until the Registrar posts the real one
The first 20 cards
Read the question, think of your answer, then open the card.
Week 1 · Bonding in organic moleculesWhat is the hybridization of each carbon in propyne, CH₃C≡CH?Show the answerHide the answer
The CH₃ carbon is sp³. The two triple-bonded carbons are sp, each with a linear geometry.
A triple bond is one sigma bond plus two pi bonds made from each carbon's two leftover p orbitals.
Week 1 · Bonding in organic moleculesWhat is the formal charge on a carbon with three bonds and one lone pair?Show the answerHide the answer
-1, a carbanion: 4 valence electrons - 2 lone-pair electrons - 3 bonds.
A carbon with three bonds and no lone pair is +1, a carbocation.
Week 1 · Bonding in organic moleculesWhich resonance contributor matters most?Show the answerHide the answer
The one with full octets, the fewest formal charges, and any negative charge on the more electronegative atom.
Resonance contributors differ only in where electrons sit; the atoms never move.
Week 1 · Functional groupsWhat functional group has a carbonyl carbon bonded directly to a nitrogen, R-CO-NR₂?Show the answerHide the answer
An amide.
Amides make up the peptide bonds that link amino acids in proteins.
Week 1 · Functional groupsWhat is the difference between an aldehyde and a ketone?Show the answerHide the answer
In an aldehyde the carbonyl carbon carries at least one hydrogen. In a ketone it is bonded to two carbons.
Week 2 · Naming organic compoundsWhat is the IUPAC name of CH₃CH(CH₃)CH₂CH₃?Show the answerHide the answer
2-methylbutane: a four-carbon chain with a methyl on carbon 2.
Number the longest chain from the end that gives the substituent the lowest number.
Week 2 · Naming organic compoundsWhat is the IUPAC name of CH₃CH₂CH(OH)CH₃?Show the answerHide the answer
Butan-2-ol (2-butanol). The chain is numbered so the OH carbon gets the lowest number.
Week 2 · Constitutional isomers and unsaturationHow many constitutional isomers have the formula C₅H₁₂?Show the answerHide the answer
Three: pentane, 2-methylbutane and 2,2-dimethylpropane.
Constitutional isomers share a formula but connect their atoms differently.
Week 2 · Constitutional isomers and unsaturationHow many degrees of unsaturation does C₆H₆ have?Show the answerHide the answer
Four, from (2C + 2 - H)/2 = (12 + 2 - 6)/2. Benzene has one ring and three double bonds.
Each ring or pi bond counts as one. Halogens count like hydrogens, and each nitrogen adds one to 2C + 2.
Week 3 · Acidity and pKaWhy is acetic acid (pKa about 4.8) so much more acidic than ethanol (pKa about 16)?Show the answerHide the answer
Acetate's negative charge is shared over two oxygens by resonance; ethoxide's sits on one. A more stable conjugate base means a stronger acid.
Week 3 · Acidity and pKaWhich features stabilize a conjugate base and so strengthen its acid?Show the answerHide the answer
Charge on a more electronegative or larger atom, resonance, nearby electron-withdrawing groups, and more s character in the orbital holding the charge.
Often remembered as ARIO: atom, resonance, induction, orbital.
Week 3 · Acidity and pKaWhich is more acidic, CH₃COOH or CF₃COOH?Show the answerHide the answer
CF₃COOH. The fluorines pull electron density away through the bonds, stabilizing the carboxylate (an inductive effect).
Trifluoroacetic acid's pKa is near 0, against about 4.8 for acetic acid.
Week 3 · Acidity and pKaWhy is a terminal alkyne (pKa about 25) far more acidic than an alkane (pKa about 50)?Show the answerHide the answer
Its C-H carbon is sp, with 50% s character, which holds the conjugate base's lone pair close to the nucleus.
An sp³ carbon has only 25% s character; an alkene's sp² carbon falls between, with a pKa near 44.
Week 3 · Acidity and pKaWill NaOH deprotonate a terminal alkyne (pKa 25), given water's pKa of 15.7?Show the answerHide the answer
No, not appreciably. Acid-base equilibria favor the side with the weaker acid, and the alkyne is a far weaker acid than water.
A stronger base, such as sodium amide (NH₃ pKa about 38), does the job.
Week 4 · Conformations of alkanesWhy is eclipsed ethane higher in energy than staggered ethane?Show the answerHide the answer
Torsional strain: in the eclipsed form the C-H bonds on neighboring carbons line up, and their electrons repel.
The barrier is about 12 kJ/mol, small enough that ethane rotates freely at room temperature.
Week 4 · Conformations of alkanesWhich conformation of butane, viewed along the C2-C3 bond, is most stable?Show the answerHide the answer
Anti, with the two methyl groups 180° apart.
Gauche, with the methyls 60° apart, is about 3.8 kJ/mol higher because the methyls crowd each other (steric strain).
Week 4 · Cyclohexane chairsWhy does a substituent on cyclohexane prefer the equatorial position?Show the answerHide the answer
An axial group bumps into the axial hydrogens two carbons away on the same face (1,3-diaxial interactions).
Methylcyclohexane is about 95% equatorial at room temperature.
Week 4 · Cyclohexane chairsWhat happens to an axial substituent when a cyclohexane chair flips?Show the answerHide the answer
It becomes equatorial, and every equatorial group becomes axial. Each group stays on the same face of the ring.
Week 4 · Cyclohexane chairsIn the most stable chair of trans-1,4-dimethylcyclohexane, where are the methyl groups?Show the answerHide the answer
Both equatorial. The trans isomer can put both groups equatorial at once, avoiding 1,3-diaxial strain.
Its ring flip would put both methyls axial, which is much less stable.
Week 5 · Chirality and stereocentersWhat makes a molecule chiral?Show the answerHide the answer
It cannot be superimposed on its mirror image. The most common cause is a carbon bearing four different groups.
Such a carbon is a stereocenter. A molecule can still be achiral if it has an internal mirror plane.
Week by week
The whole deck: 47 cards over 10 weeks. Every week is open from day one.
- 1Bonding and functional groups5 cards
- Bonding in organic molecules 3
- Functional groups 2
- 2Naming and isomers4 cards
- Naming organic compounds 2
- Constitutional isomers and unsaturation 2
- 3Organic acids and bases5 cards
- Acidity and pKa 5
- 4Conformations5 cards
- Conformations of alkanes 2
- Cyclohexane chairs 3
- 5Chirality4 cards
- Chirality and stereocenters 2
- R and S configuration 2
- 6Stereoisomers5 cards
- Enantiomers, diastereomers and meso compounds 3
- Optical activity 2
- 7Infrared and mass spectrometry5 cards
- Infrared spectroscopy 3
- Mass spectrometry 2
- 8NMR spectroscopy5 cards
- Proton NMR 4
- Carbon-13 NMR 1
- 9Substitution5 cards
- SN1 and SN2 reactions 5
- 10Elimination4 cards
- E1 and E2 reactions 4