4. Organic Compounds: Cycloalkanes and their Stereochemistry

Question 1

are saturated cyclic hydrocarbons

Have the general formula (CnH2n)

Answer 1

Cycloalkanes

Question 2

Cycloalkanes are less flexible than open-chain alkanes; Much less conformational freedom in
cycloalkanes

Question 3

same connections, different three-dimensional geometry

Answer 3

Stereoisomers

Question 4

Rings larger than 3 atoms are not flat

Question 5

can assume nonplanar
conformations to minimize angle strain and torsional
strain by ring-puckering

Answer 5

Cyclic molecules

Question 6

Larger rings have many more possible conformations
than smaller rings and are more difficult to analyze

Question 7

Baeyer (1885): since
carbon prefers to have bond angles of
approximately 109°,
ring sizes other than
five and six may be too strained to exist

Question 8

expansion or compression of bond
angles away from most stable

Answer 8

Angle strain

Question 9

eclipsing of bonds on neighboring
atoms

Answer 9

Torsional strain

Question 10

repulsive interactions between
nonbonded atoms in close proximity

Answer 10

Steric strain

Question 11

3 carbon or even 4 carbon rings can undergo addition reaction because of so much ring strain

Question 12

cyclopropane - least stable

cyclohexane - most stable

Question 12

Symmetrical with C–C–C bond angles of 60°

Requires that sp3
based bonds are bent (and
weakened)

All C-H bonds are eclipsed

Answer 12

Cyclopropane

Question 13

has less angle strain than cyclopropane
but more torsional strain because of its larger number
of ring hydrogens

slightly bent out of the plane; bend increases angle strain but decreases torsional strain

Answer 13

Cyclobutane

Question 14

have no angle strain but very high torsional strain; Actual conformations of cyclopentane are nonplanar, reducing torsional strain

Answer 14

Cyclopentane

Question 15

is free of angle strain and
torsional strain

Answer 15

Cyclohexane

Question 16

The conformation has alternating atoms in a common plane and tetrahedral angles between all
carbons

Answer 16

Chair conformation

Question 17

Hydrogen atoms of the axial methyl group on
C1 are too close to the axial hydrogens three carbons away on C3 and C5, resulting in 7.6
kJ/mol of steric strain

Answer 17

1,3-diaxial interaction

Question 18

equatorial positions give more stable isomer

Question 19

axial to equatorial

equatorial to axial

up-up

down-down

Question 20

form a to b = clockwise

form b to a = counterclockwise