1-8 structural o chem

Question 1

enantiomers

Answer 1

mirror images.
non superimposable
no plane of symmetry

Question 2

diastomers

Answer 2

no plane of symmetry
not all chiral centres have change

Question 3

interatomic bonding

Answer 3

Different interatomic distances,
so different dipole moments, melting points,
boiling points, IR and NMR spectra,
solubilities, chromatographic properties etc

Question 4

chirality can arise from

Answer 4

a “chiral axis” where A= A’ are not equal

Question 5

for chiral axis molecules what does the ability to inconvert mean?

Answer 5

One of the transition states is accessible, \ mirror image forms can interconvert

Question 6

transition states are

Answer 6

achiral

Question 7

steric clashes

Answer 7

high energy

Question 8

BINAP

Answer 8

stable. cannot interconvert

Question 9

allenes

Answer 9

Two double bonds with a common carbon – each bond needs a different p orbital so
planes must be orthogonal.

Question 10

amines are achiral as

Answer 10

lone pair can interconvert to mirror image
Pyramidal N is not usually a stereogenic centre, due to rapid inversion

Question 11

P groups cannot as

Answer 11

more core electrons. cannot inverconvert Pyramidal P can be a stereogenic centre, enantiomers can arise

Question 12

how to calculate the number of potential wells

Answer 12

3N-6 dimensions, where N = no. of atoms

Question 13

rotations give what

Answer 13

Rotation gives an infinite number of conformation

Question 14

what is a conformer

Answer 14

Different shapes possible for a single molecule (usually related by rotations about single bonds)

Question 15

what are conformer

Answer 15

conformations at the lowest energy

Question 16

torsion bond

Answer 16

bond between two chemical bonds

Question 17

syn-periplanar

Answer 17

maxima / eclipsed 0

Question 18

anticlinal

Answer 18

60 lower/second minima staggered

Question 19

gauche

Answer 19

120 eclipsed maxima

Question 20

anti-periplanar

Answer 20

180 true mimina / eclipsed

Question 21

gauche

Answer 21

240 eclipsed maxima

Question 22

difference between different conformers

Answer 22

difference between conformers is
temperature.

Question 23

calculate K relating to conformers

Answer 23

K = [anti-periplanar] /
[gauche]
= e ^ -G/RT

Question 24

why does R point away from R2 in esters and amides

Answer 24

Steric effect between Rs and overlap between lone pairs and empty σ* (overlap between full and empty orbitals is always stabilising).

Question 25

ester N is more electropositive than O therefore…

Answer 25

the resonance structure has a greater influence so much that it can appear in H NMR

Question 26

what is prefered for amides, Z or E?

Answer 26

Z far more stable (steric + some electronic effect?) Only one set of signals in NMR, structures predictable

Question 27

Baeyer strain.

Answer 27

Strain due to distorted bond angle θ

Question 28

3 rings are

Answer 28

planar

Question 29

when the internal angle is lower tha 109 what does this mean?

Answer 29

raised energy

Question 30

talk about whether bent or planar conformations are prefered for 4 rings structures

Answer 30

For bent conformation, θ < 90o, so Baeyer strain increases but Planar conformation suffers from Pitzer strain
– strain due to suboptimal torsion angle . bent is then prefered. as Lower Pitzer strain compensates for increased Baeyer strain

Question 31

7 membered rings have

Answer 31

but still some Pitzer strain even with their Most stable conformation, same with 8.

Question 32

staggered conformations

Answer 32

Overlap of filled orbital with empty
orbital is always a stabilising factor
(lowers energy)

Question 33

eclipsed conformation

Answer 33

Overlap of filled orbitals is always a
destabilising factor (raises energy).

Question 34

what influences conformation changes ?

Answer 34

energy barrier if it is small there will be many interconversions