Organic 3: Alkanes/Cycloalkanes - Conformations & cis-trans Stereoisomers

Question 1

Conformations

Answer 1

different spatial arrangements of a molecule that are generated by rotation about single bonds

Question 2

Conformational analysis

Answer 2

study of how conformational factors affect the structure of a molecule and its properties

Question 3

Staggered conformation

Answer 3

each C-H bond of one carbon bisects an H-C-H angle of the other carbon

Question 4

Eclipsed conformation

Answer 4

each C-H bond of one carbon is aligned with a C-H bond of the other carbon

Question 5

Gauche

Answer 5

spatial relationship term used when the torsion angle is 60 degrees

Question 6

Anti

Answer 6

spatial relationship term used when the torsion angle is 180 degrees

Question 7

Torsional strain

Answer 7

conformations in which the torsion angles between adjacent bonds are other than 60 degrees

Question 8

Steric strain

Answer 8

torsional and other sources of strain in molecules

Question 9

Activation energy

Answer 9

the minimum energy that a reacting system must possess above its most stable state in order to undergo a chemical or structural change

Question 10

Transition state

Answer 10

the point of maximum potential energy encountered in reactants as they proceed to products

Question 11

van der Waals strain (steric hindrance)

Answer 11

destabilization of a molecule that results when 2 of its atoms are too close to each other; contributes to the total steric strain

Question 12

Strain energy

Answer 12

deviations from the ideal values for bond angles/distances, etc will destabilize a particular structure and increase its potential energy

Question 13

Angle strain

Answer 13

strain a molecule has because one or more of its bond angles deviate from the ideal value

Question 14

Envelope

Answer 14

Nonplanar conformation of cyclopentane in which 4 of the carbon atoms are coplanar; the 5th carbon is out of the plane of the other 4

Question 15

Half-chair

Answer 15

Nonplanar conformation of cyclopentane in which there are 3 coplanar carbons, with 1 carbon atom displaced above that plane and another below it

Question 16

Chair conformation

Answer 16

most stable conformation of cyclohexane; with C-C-C bond angles of 111 degrees, it is nearly free of angle strain; all of its bonds are staggered, making it free of torsional strain as well

Question 17

Boat

Answer 17

much less stable nonplanar conformation of cyclohexane; bond angles are approximately tetrahedral; relatively free of angle strain; destabilized by torsional strain associated with eclipsed bonds on 4 of its carbons; two “flagpole” hydrogens contribute a small amount of van der Waals strain as well

Question 18

Twist boat (skew boat)

Answer 18

more stable nonplanar conformation of cyclohexane; reduces both torsional strain and van der Waals strain by a rotation about the carbon-carbon bond

Question 19

Axial hydrogens

Answer 19

6 of cyclohexane’s hydrogens have their bonds parallel to a vertical axis that passes through the ring’s center; alternately directed up or down on adjacent carbons

Question 20

Equatorial hydrogens

Answer 20

6 of cyclohexane’s hydrogens are located approximately along the equator of the molecule; 4 bonds to each carbon are arranged tetrahedrally

Question 21

Ring inversion (chair-chair interconversion)

Answer 21

one chair conformation is converted to another chair

Question 22

Intermediate

Answer 22

not a potential energy maximum, but a local minimum on the potential energy profile

Question 23

1,3-diaxial repulsions

Answer 23

repulsive forces between axial substituents on the same side of a cyclohexane ring

Question 24

Standard free energy

Answer 24

one of the fundamental equations of thermodynamics concerns systems at equilibrium and relates the equilibrium constant K to the difference in this between the products and the reactants

Question 25

cis

Answer 25

when substituents are on the same side they are ___ to each other

Question 26

trans

Answer 26

when substituents are on opposite sides they are ___ to each other

Question 27

Stereoisomers

Answer 27

isomers that have their atoms bonded in the same order (same constitution) but they differ in the arrangement of atoms in space; those of the cis-trans type are sometimes referred to as geometric isomers

Question 28

Polycyclic

Answer 28

compounds that contain more than 1 ring

Question 29

Spiro

Answer 29

a compound with one atom common to 2 rings

Question 30

Bridged

Answer 30

compound with 2 atoms common to 2 or more rings

Question 31

Heterocyclic compound

Answer 31

a substance with a ring that contains at least one heteroatom