Cycloalkanes

Question 1

what is a cycloalkane

Answer 1

cyclic hydrocarbon (all sp3) with the general formula CnH2n

Question 2

naming

Answer 2

prefix cyclo- alkane

Question 3

sigma bond rotation

Answer 3

fixed, never 360 degrees

Question 4

faces

Answer 4

rings have distinct tops and bottoms

Question 5

cis

Answer 5

substituents pointed in the same direction/side

Question 6

trans

Answer 6

substituents pointed in the opposite direction/side

Question 7

properties

Answer 7

nonpolar, fairly unreactive

Question 8

bp/mp

Answer 8

cyclic has higher than straight chain, more rigid, more surface area, stacks better

depends on MW (higher = higher)

Question 9

ring conformations suffer from

Answer 9

torsional/eclipsing strain

steric strain

weird bond angles/angle strain

Question 10

combustion

Answer 10

smaller rings release more energy, more strain

more energy released than straight chains

Question 11

cyclopropane

Answer 11

ring strain 27.6 kcal/mol

has bond strain, torsional strain

planar

BDE higher than cyclobutane

Question 12

cyclobutane

Answer 12

ring strain 26.3 kcal/mol

has bond strain/torsional strain

puckered

BDE 63

Question 13

cyclopentane

Answer 13

ring strain 6.5 kcal/mol

has bond strain, LESS torsional strain

envelope

BDE 81

Question 14

cyclohexane

Answer 14

ring strain 0.1 kcal/mol

has bond strain, NO torsional strain

chair

BDE 88

Question 15

why does cyclopropane have higher BDE than cyclobutane?

Answer 15

cyclopropane C-C bond is shorter + stronger (1.51) than C-C bond in cyclobutane (1.551)

hyperconjugation in cyclopropane means it competes for e- donation, but not in cyclobutane

Question 16

cyclohexane’s chair conformation

Answer 16

no eclipsing

bond angle is almost 109.5

bond strength is approx. that of straight chains

Question 17

torsional/eclipsing strain

Answer 17

repulsion of e- in orbitals as they pass each other in close quarters (eclipse); resistance to bond rotation

Question 18

steric strain

Answer 18

2 groups cannot occupy the same space; bump into each other

Question 19

bond angle strain

Answer 19

weird bond angles deviated from normal 109.5 tetrahedral

energy required to distort the bonds

Question 20

structural/constitutional isomer

Answer 20

same molecular formula, different atom connectivities

Question 21

stereoisomer

Answer 21

same molecular formula, same connectivity, different atom arrangement in space

Question 22

geometric isomer

Answer 22

specific type of stereoisomer; cis & trans