CHEM 140A Lecture Notes - Lecture 6: Cyclobutane, Radiocarbon Dating, Cyclopentane

• School: UCSD
• Department: Chemistry and Biochemistry
• Course: CHEM 140A
• Professor: Joseph M Oconnor

Document Summary

H comb(calculated ) h comb( experimental: almost no strain in 6-carbon and 14-carbon. 5-carbon has more strain than 6-carbon despite being closer to ideal angle because 5-carbon is more planar (thus eclipsing strain), but 6-carbon is more puckered. Be able to draw puckered for 4-, 5-, and 6-carbon. 5-carbon is called envelope conformer, looks like envelope. Types of strain: bond angle strain (especially in small rings, eclipsing strain, transannular strain (especially in medium-sized rings) Cyclobutane: 4-carbon ring, 90 if flat, puckering reduces eclipsing, make a square, then lift one corner a bit. Cyclopentane: 5-carbon ring, 108 if flat. Cyclohexane: 6-carbon ring, most stable conformer: chair conformer. Make a hexagon, then lift one corner, lower the one next to it, then lift, then lower, etc. Axial: perpendicular to plane of the hexagon. Equatorial: (almost) in the plane o the hexagon: boat conformer. Make a hexagon, lift two opposite points. Has transannular (steric) repulsion between hydrogens of the two lifted.