Organic Chemistry Unit 2

constitutional isomers

compounds that have the same molecular formula, but different molecular connectivity

stereoisomers

compounds that have the same molecular formula and same molecular connectivity, but a different spatial arrangement of the atoms. enantiomers and diastereomers are sub-classes of stereoisomers

diastereomers

stereoisomers that can never be related by a mirror plan relationship

eclipsed vs. staggered conformations

rotating the atoms on one carbon by 60 degrees converts an eclipsed conformation into a staggered conformation and vice versa

staggered conformation

more stable than an eclipsed conformation

gauche conformation

generally higher in energy than an anti conformation

anti conformation

the more stable staggered arrangement, compared with gauche

Sn2 mechanism

involves one step and occurs with inversion of configuration

Sn2 stereochemistry

displacement occurs with inversion of configuration

good leaving group

the conjugate bases of strong acids are good leaving groups

polar protic solvent

capable of intermolecular hydrogen bonding

Sn1 mechanism

involves 2 steps and occurs fastest with tertiary alkyl halides

Sn1 rate-determining step

breaking the bond between carbon and the leaving group to generate a carbocation

carbocation geometry

the central carbon is sp2 hybridized, has trigonal planar geometry, and has an empty p orbital

constitutional isomers vs. stereoisomers

constitutional isomers have different connectivity; stereoisomers have the same connectivity but different spatial arrangements

diastereomers

the cis and trans versions of the same substituted cycloalkane are diastereomers

angle strain

cyclopropane has bond angles of approximately 60 degrees, rather than the ideal 109.5 degrees for sp3 carbon

torsional strain

repulsion between eclipsing bonds, such as H-H interactions in cyclopropane

steric strain

repulsion between groups that are close together in space

1,3- diaxial interactions

steric repulsion involving axial groups on a cyclohexane chair

axial vs. equatorial positions

a ring flip exchanges axial and equatorial positions. the equatorial position is generally favored by bulky substituents

chair conformation stability

conformations with substituents in equatorial positions are generally more stable than those with bulky axial substituents

cis 1,2

1 axial- 1 equatorial

cis 1,3

both equatorial or both axial

cis 1,4

1 equatorial, 1 axial

1,2 trans

both axial or both equatorial

trans 1,3

1 axial, 1 equatorial

1,4 trans

both axial or both equatorial

(R,R) vs. (S,S)

enantiomers

(R,S) vs. (S,R) chiral

enantiomers

(R,R) vs. (R,S)

diastereomers

(R,S) vs. (R,S)

identical

(R, S) vs. (S, R) achiral

meso-compound