Cycloalkanes

A cycloalkane is an alkane whose carbon atoms are arranged cyclically (i.e. in a ring).

• effectively non-polar compounds
• general formula of $C_nH_{2n}$ where $n \geq 3$

Angle strain is significant in both compounds

A sterically demanding eclipsed conformation is dominant for both compounds. The resulting ring strain is pronounced; both compounds are highly unstable.

The angle strain in both of these geometries

Both compounds can alleviate their torsional strain by rotating about their C-C bonds; a puckered conformation. As a result, the ring strain is effectively eliminated, and both are stable species.

Conformational Isomers

To alleviate ring strain (i.e. angular repulsion and torsional strain), cyclohexane adopts an energetically stable chair conformation by rotating about its C-C bonds.

All bond angles are 109.5 and all H atoms on adjacent carbons are staggered

To draw chair conformers efficiently and accurately, follow the rules in Tables 8.2 and 8.3

Configurational Isomers

Disubstituted cycloalkanes may exhibit configurational isomerism

• the ring freezes the geometry and preserves the distinct spatial rel. between substituents
• cycloalkanes with subs. on two or more ring $\ce{C}$ atoms are classified as cis-trans isomers

Identifying a geometric isomer:

1. is there a ring
2. are there at least 2 subs.
3. are those 2 subs on different sp2 orbitals (i.e. $\ce{C}$ atoms) on the ring