Structure and Stability

Question 1

saturated

Answer 1

if a compound contains no pi bonds and no rings, will have 2n+2 hydrogen atoms

Question 2

unsaturated

Answer 2

a compounds has at least one pi bond or a ring, will have fewer than 2n+2 hydrogen atoms

Question 3

degree of unsaturation (d)

Answer 3

(2n+2-x)/2 (x is the number of hydrogens and any monovalent atoms, oxygen has no effect, replace each N with 1 C and 1 H)

Question 4

inductive effects

Answer 4

the stabilization of reaction intermediates by sharing of electrons through sigma bonds

Question 5

electron-withdrawing groups

Answer 5

pull electrons toward themselves through sigma bonds, can stabilize e- rich regions

Question 6

electron-donating groups

Answer 6

push electron density away from themselves through sigma bonds, can stabilize e- deficient regions

Question 7

resonance effects

Answer 7

stabilize charge by delocalization through pi bonds

Question 8

conjugated system

Answer 8

contains three or more atoms that each bear a p orbital and are aligned parallel to one another, creating the possibility of delocalized electrons

Question 9

localized

Answer 9

electrons that are confined to one orbital; either a bonding orbital between atoms or a lone pair orbital

Question 10

delocalized

Answer 10

electrons that can interact with orbitals on adjacent atoms

Question 11

resonance hybrid

Answer 11

the average of all resonance contributors

Question 12

strength of an acid refers to:

Answer 12

the degree to which it dissociates (or donates its proton) in solution

Question 13

the strength of the acid is determined by:

Answer 13

the extent to which the negative charge on the conjugate base is stabilized

Question 14

nucleophiles

Answer 14

species that have unshared pairs of electrons or pi bonds and, frequently, a negative charge. “nucleus-loving”

Question 15

nucleophiles are also known as:

Answer 15

Lewis bases (electron-pair donators)

Question 16

nucleophilicity

Answer 16

a measure of how strong a nucleophile is, or how easily it can donate an e- pair

Question 17

what are some trends in nucleophilicity?

Answer 17

CARIO

Question 18

polarizability

Answer 18

how easy it is for the electrons surrounding an atom to be distorted, larger atoms are generally more polarizable and thus more nucleophilic. generally apply down columns in the periodic table.

Question 19

electrophile

Answer 19

electron-deficient species that often have a positive charge and an incomplete octet. “electron-loving”

Question 20

electrophilicity

Answer 20

a measure of how strong an electrophile is, or how well it can accept an electron pair

Question 21

electrophiles are also known as:

Answer 21

Lewis acids (electron-pair acceptors)

Question 22

what determines a good leaving group?

Answer 22

they are more likely to dissociate from their substrate because they are more stable in solution. Ex. weak bases, large atoms, less charged/uncharged

Question 23

ring strain

Answer 23

arises when bond angles between ring atoms deviate from the ideal angle predicted by the hybridization of the atoms. the strain weakens carbon-carbon bonds and increases reactivity

Question 24

what are conditions required for hydrogenation reactions?

Answer 24

heat (120 degrees Celsius), H2, Ni, a ring structure with ring strain (ex. cyclopropane, cyclobutane)

Question 25

constitutional isomers

Answer 25

compounds that have the same molecular formula but different connectivity

Question 26

conformational isomers

Answer 26

compounds that have the same molecular formula and connectivity, but differ from on another by rotation about a sigma bond (ex. staggered vs. eclipsed)

Question 27

which conformation (staggered, eclipsed) is more stable and why?

Answer 27

staggered is more stable because it has less electronic repulsion and less steric hindrance

Question 28

what conformation has the absolute maximum potential energy?

Answer 28

syn conformation

Question 29

what conformation has the absolute minimum potential energy?

Answer 29

anti conformation

Question 30

in the chair conformation, why do larger groups prefer to be in the equatorial axis?

Answer 30

to reduce 1,3-diaxial interactions

Question 31

stereoisomers

Answer 31

molecules that have the same molecular formula and connectivity but differ in the spatial arrangement of the atoms (cannot be interconverted by rotation about sigma bonds)

Question 32

chiral

Answer 32

any molecule that cannot be superimposed on its mirror image

Question 33

achiral

Answer 33

a molecule that can be superimposed on its mirror image, has a plane of symmetry

Question 34

stereocenter/stereogenic centre/asymmetric centre

Answer 34

a carbon atom that is a chiral centre and attached to four different groups

Question 35

absolute configuration

Answer 35

R/S configuration assigned to chiral centres

Question 36

absolute configuration R

Answer 36

clockwise

Question 37

absolute configuration S

Answer 37

counter-clockwise

Question 38

enantiomers

Answer 38

non-superimposable mirror images, can occur when chiral centres are present

Question 39

what are some properties of enantiomers?

Answer 39

will always have opposite absolute configurations, will have many identical physical properties, opposite rotation of plane-polarized light (optical activity)

Question 40

what is an important property that differs between enantiomers?

Answer 40

the manner in which they interact with plane-polarized light

Question 41

optically active

Answer 41

a compounds that rotates the plane of polarized light

Question 42

dextrorotatory (d), (+)

Answer 42

a compound that rotates plane-polarized light clockwise

Question 43

levorotatory (l), (-)

Answer 43

a compound that rotates plane-polarized light counterclockwise

Question 44

specific rotation

Answer 44

the magnitude of rotation of plane-polarized light for any compound

Question 45

what does specific rotation depend on?

Answer 45

the structure of the molecule, the concentration of the sample, the path length through which the light must travel

Question 46

a pair of enantiomers will rotate plane-polarized light with:

Answer 46

equal magnitude but opposite directions

Question 47

racemic mixture

Answer 47

a 50/50 mixture

Question 48

racemate

Answer 48

a racemic mixture of enantiomers

Question 49

what is a property of a racemate/racemic mixture of enantiomers?

Answer 49

it is not optically active

Question 50

is there a relationship between configuration (R/S, alpha/beta) and optical activity (+)/(-)?

Answer 50

NO

Question 51

if n is the number of chiral centres, how do you determine the number of possible stereoisomers?

Answer 51

2^n

Question 52

diastereomer

Answer 52

stereoisomers that are non-superimposable, non-mirror images

Question 53

what are some of the properties between diastereomers?

Answer 53

different physical and chemical properties, no predictable relationship between the specific rotations of diastereomers

Question 54

how do you separate enantiomers (lab process)?

Answer 54

RESOLUTION (use an enantiomerically pure chiral probe that associates with the components of the mixture through either covalent bonds or intermolecular forces to create diastereomers with different physical properties, allows for separation by filtration, work-up step generates the isolated enantiomerically pure product)

Question 55

epimers

Answer 55

a sub-class of diastereomers that differ in their absolute configuration at a single chiral centre

Question 56

anomer

Answer 56

epimers that form as a result of ring closure

Question 57

anomeric centre/anomeric carbon

Answer 57

the carbon/chiral centre that distinguishes the two anomers

Question 58

alpha configuration

Answer 58

hydroxyl group is down

Question 59

beta configuration

Answer 59

hydroxyl group is up

Question 60

meso compound

Answer 60

have chiral centres but are not optically active (achiral) because there is an internal plane of symmetry

Question 61

geometric isomers

Answer 61

diastereomers that differ in orientation of substituents around a ring or a double bond (constrained by geometry and cannot rotate freely, fixed configuration)

Question 62

cis configuration

Answer 62

two longer alkyl chains are on the same side of the molecule

Question 63

trans configuration

Answer 63

two longer alkyl chains are on opposite sides of the molecule

Question 64

(Z) configuration

Answer 64

higher priority groups are on the same side of the double bond

Question 65

(E) configuration

Answer 65

higher priority groups are on opposite sides of the double bond