Unit 4

Question 1

Constitutional isomers

Answer 1

molecules with the same chemical formula, but different connectivity

Question 2

Conformational isomers

Answer 2

molecules with the same formula and connectivity, but occupy a different 3D space due to rotation around a sigma bond

Question 3

Gauche

Answer 3

60º

Question 4

Eclipsed

Answer 4

directly in back of

no matter which atoms/molecules are where, this is always a higher energy level than gauche or anti

Question 5

Anti

Answer 5

180º

the most stable when the largest constituents are 180º away from each other

Question 6

Enantiomers

Answer 6

non-superimposible mirror images of eachother

Question 7

What did the example with 2-bromobutane show?

Answer 7

that depending on the possible configurations, sometimes a conformational change can make a superimposible mirror image but sometimes it can not

Question 8

Do enantiomers have to have the same configuration?

Answer 8

No

For example, 2-bromobutane had two different configurations that made an enantiomer

Question 9

Chiral

Answer 9

a molecule with a nonsuperimposable mirror image

Question 10

Criteria for chiral

Answer 10

1. does the molecule have a single asymmetric carbon? If yes, its chiral
2. does the molecule have internal mirror plane/symmetry? If yes, its achiral

Question 11

How to assign R and S configuration

Answer 11

1. orient the molecule so lowest priority group goes into the plane (hydrogen normally)
2. assign the priorities of the 3 remaining groups based on atomic mass
3. look at counter clockwise vs. clockwise

Question 12

S-configuration

Answer 12

goes counter clockwise

Question 13

R-configuration

Answer 13

goes clockwise

Think: r = “right”

Question 14

Does a conformational change result in a configurational change?

Answer 14

No.

You can rotate about the sigma bonds, but R and S configuration will still remain the same

Question 15

What to check for after you have determined that two molecules are the same molecules with the same connectivity?

Answer 15

Check for if they actually have the same configuration just rotated in space

Question 16

Configurational isomers with a non-superimposable mirror image

Answer 16

enantiomers

Question 17

Configurational isomers with a superimposable mirror image

Answer 17

disastereomers

Question 18

Stereoisomers

Answer 18

isomers with the same constitution but that differ in the respect to the arrangement of their atoms in space

Question 19

Disastereomers

Answer 19

stereoisomers that have different configurations at one or more (but not all) of the equivalent asymmetric carbon centers and are NOT mirror images

Question 20

Geometric

Answer 20

also called cis-trans isomerism

stereoisomers that involve a ring or double bond

identical substituents can either be on the same side or opposite sides of the bond or ring

Question 21

As bond length increases what happens to dipole moment?

Answer 21

decrease

inverse relationship between bond length and dipole moment

Question 22

Why are intramolecular covalent bonds stronger than intermolecular dipole-dipole bonds?

Answer 22

electrons are shared in a bond between two nuclei. this creates a strong force of attraction.

a dipole-dipole bond is only attracted to a partially positive/partially negative species. also, occur at further distances.

Question 23

What is the strongest bond?

Answer 23

ionic

Question 24

Hydrogen bonding donor

Answer 24

polar species that contains a H that is covalently bonded to an O, F, or N

Question 25

Hydrogen bonding acceptor

Answer 25

any polar species with a lone electron pair on O, F, or N

*does not need a H atom, since this will be donated to it

Question 26

Adhesive forces

Answer 26

forces between UNLIKE molecules

Question 27

Cohesive forces

Answer 27

forces between LIKE molecules

Question 28

Forces in chain molecules vs. branched molecules

Answer 28

in branched molecules, electrons can get closer together and potential energy increases.

therefore, chained molecules have stronger forces and higher boiling points because they have less PE and greater Force of Attraction to overcome

Question 29

What do dispersion forces occur due to?

Answer 29

polarized e- clouds

therefore, larger molecules have greater intermolecular attractions

Question 30

Dipole-dipole interactions

Answer 30

occur between two polar molecules

Question 31

What is hydrogen a form of?

Answer 31

dipole-dipole interactions

Question 32

Ex: if both ICl and Br2 have a dipole moment how can you tell which is stronger?

stronger = higher boiling point

Answer 32

Br2 only has a temporary dipole because there is no different in electronegativity

therefore, ICl will be stronger since it has dispersion forces and a permanent dipole

Question 33

What causes temporary dipoles? (dispersion forces)

Answer 33

random fluctuations in e- clouds distributions

Question 34

Polarizable

Answer 34

larger molecules have more polarizable e- clouds which makes them form stronger dispersion forces

Question 35

What is another name for a stereoisomer?

Answer 35

constitutional isomer

Question 36

Is a conformational isomer a stereoisomer?

Answer 36

no

Question 37

Is a conformational isomer the same molecule?

Answer 37

yes.

it is just rotated around a sigma bond differently

Question 38

Is a configurational isomer the same molecule?

Answer 38

no

have to physically move something on the same carbon

Question 39

Is a constitutional isomer the same molecule?

Answer 39

no

there is different connectivity

Question 40

Criteria for an enantiomer

Answer 40

1. determine that it is a configurational isomer
2. look at asymmetric carbons
3. enantiomers have to have exact opposite configuration

ex: R S // S R

Question 41

Are enantiomers chiral?

Answer 41

yes

Question 42

Meso compound

Answer 42

referring to mirror image in ONE compound

two asymmetric carbons

one with R and one with S

this makes an internal plane of symmetry and ACHIRAL

Question 43

An entaniomer with a single asymmetric center has a R configuration. What does the other isomer have to be?

Answer 43

has to have an S configuration