Study guides › C/P › Organic Chemistry
Alkanes & Conformations
Alkanes are the simplest organic molecules, but their shapes drive many exam questions. You will predict physical properties, follow radical halogenation, read Newman projections and energy graphs, and analyze cyclohexane chairs.
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What this chapter covers
- Alkane Structure & Physical Properties. Boiling-point ranking and combustion questions all come down to one idea: alkanes only feel London dispersion forces.
- Free-Radical Halogenation of Alkanes. Alkanes react only under harsh conditions, and the classic example is halogenation. Know the chain steps and why bromine is more selective than chlorine.
- Newman Projections & Acyclic Conformations. Newman projections and the torsional energy graph appear often. Know which conformer is highest and lowest, and why.
- Cycloalkanes & Ring Strain. Small rings are strained and reactive, and cyclohexane is not. Know why, and how heats of combustion measure it.
- Chair Cyclohexane, Axial/Equatorial & Ring Flip. Chair drawings, A-values, and disubstituted cyclohexane stability are among the most testable ideas in this chapter.
Key points to know
- Alkanes: only C–C and C–H σ bonds, sp³ carbons
- London dispersion is the only intermolecular force
- Radical chain: initiation, propagation, termination
- Propagation steps regenerate the radical
- Staggered is lower than eclipsed by torsional strain
- Butane order: anti < gauche < eclipsed < fully eclipsed
- Ring strain = angle + torsional + steric strain
- Cyclopropane is planar with 60° angles: about 27 kcal/mol
Try a practice question
Which intermolecular force operates between alkane molecules?
- Hydrogen bonding
- Dipole–dipole attraction
- London dispersion forces
- Ion–dipole attraction
Show the answer
C. Alkanes are nonpolar and have no O–H or N–H bonds, so only temporary induced dipoles (London dispersion) act between them.
Common questions
What does this chapter cover?
Alkanes & Conformations covers Alkane Structure & Physical Properties, Free-Radical Halogenation of Alkanes, Newman Projections & Acyclic Conformations, Cycloalkanes & Ring Strain, Chair Cyclohexane, Axial/Equatorial & Ring Flip.
What should I know first?
Alkanes: only C–C and C–H σ bonds, sp³ carbons London dispersion is the only intermolecular force Radical chain: initiation, propagation, termination
23 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.