Exam 2 (Ch 3, 5, 14, 15)

Question 1

what is a bronsted acid

Answer 1

proton donor

Question 2

what is a bronsted base

Answer 2

proton acceptor

Question 3

what does a bronsted acid look like

Answer 3

H attached to EN atom

Question 4

what can a bronsted acid do?

Answer 4

stabilize a negative charge

Question 5

what do you look for when looking for bronsted bases?

Answer 5

a negative charge and localized lone pairs

Question 6

what is a conjugate acid

Answer 6

a protonated base

Question 7

what is a conjugate base

Answer 7

a deprotonated acid

Question 8

what do strong bases form?

Answer 8

weak conjugate acids

Question 9

what do strong acids form?

Answer 9

weak conjugate bases

Question 10

why do strong acids form weak conjugate bases?

Answer 10

because they really want to give up that proton, don’t want it back

Question 11

why do strong bases form weak conjugate acids?

Answer 11

because they really want to take a proton, don’t want to give it up once they get it

Question 12

what does the equilibrium of an acid-base reactio always favor?

Answer 12

the side with the higher, more positive pka value (weaker acid and weaker base)

Question 13

when using ARIO to analyze the strength of an acid or determine equilibrium, what are you comparing?

Answer 13

the stability of the conjugate base

Question 14

what is the ability to stabilize a negative charge proportional to?

Answer 14

the stability of a conjugate base which leads to a stronger acid!

Question 15

what does ARIO stand for?

Answer 15

Atom: electronegativity and size
Resonance
Induction
Orbital

Question 16

which is better able to stabilize a negative charge, resulting in a more stable conjugate base and a stronger acid, sp or sp3 hybridized orbital? why?

Answer 16

sp hybridized is better because more s character holds negative charge closer to nucleus = more stable

Question 17

when identifying the most acidic hydrogen in a compound, what 3 atoms do you look for attached hydrogens on first? how do you find if those 3 are not present?

Answer 17

Sulfur, Oxygen, and Nitrogen; if not present, look for resonance, induction, or hybridized orbitals

Question 18

define constitutional isomers

Answer 18

same molecular formula, different connectivity

Question 19

define stereoisomers

Answer 19

same MF, same connectivity, different spatial arrangement

Question 20

what are the 3 types of stereoisomers?

Answer 20

1. ring
2. double bond
3. chirality stereoisomers

Question 21

how do you assign configuration for ring stereoisomers?

Answer 21

cis: all wedges or all dashes, groups on same side
trans: wedge and dash mixed up, groups on different sides

Question 22

is there any rotation in ring stereisomers? why or why not?

Answer 22

no rotation, bonds locked into place

Question 23

how do you assign configuration for double bond stereoisomers?

Answer 23

cis: 2 identical groups on SAME side of double bond
trans: 2 identical groups on OPPOSITE side of double bond

Question 24

are double bonds rotatable? why or why not?

Answer 24

no rotation, P orbitals must remain parallel so pi bond doesn’t break

Question 25

how do you assign configuration of 2 identical groups are on the same END of a double bond? is cis/trans stereoisomerism possible here?

Answer 25

no cis/trans! Z: 2 higher priority groups on the same side of DB (like cis) E: 2 higher priority groups on opposite side of DB (like trans)

Question 26

what determines higher priority?

Answer 26

larger atomic number

Question 27

how do you assign R/S configuration of chiral centers?

Answer 27

1. assign priority to each of the 4 groups 2. make sure lowest priority is on a dash!! 3. draw path from 1-2-3 clockwise: (R) counterclockwise: (S)

Question 28

how do you assign D/L configuration for Fischer projections?

Answer 28

analyze bottom-most carbohydrate OH on Left: L OH on right: D

Question 29

do chiral molecules have an optical rotation value?

Answer 29

yes!

Question 30

what do chiral molecules possess?

Answer 30

non super-imposable mirror images

Question 31

what is an enantiomer?

Answer 31

a chiral compound's one non super-imposable mirror image

Question 32

when do chiral molecules exist?

Answer 32

when a carbon is attached to 4 DIFFERENT groups

Question 33

what is a racemic mixture?

Answer 33

a 50/50 mixture or both enantiomers of a compound (usually costs too much to separate. so lump all together and you're fine)

Question 34

what are the only 2 differences between enantiomers?

Answer 34

1. optical rotation of each | 2. how each interacts with other molecules (smell and thalidimide babies)

Question 35

what are diastereomers?

Answer 35

non super-imposable and also NOT mirror images

Question 36

which can be distinguised by chemical properties: enantiomers or diastereomers?

Answer 36

diastereomers

Question 37

what are meso compounds?

Answer 37

possess a chiral center but also have a plane of symmetry, so ACHIRAL

Question 38

do meso compounds have optical rotation?

Answer 38

nope!

Question 39

what does NMR stand for?

Answer 39

Nuclear Magnetic Resonance

Question 40

what does NMR mean?

Answer 40

nucleus of an atom is in a magnetic field and it resonates by absorbing radiofrequency

Question 41

what kind of nuclei can spin? (2)

Answer 41

1. odd atomic number 2. odd mass number just need to have one

Question 42

what is it called when a nucleus can spin?

Answer 42

NMR active

Question 43

what is the most commonly observed NMR nucleus?

Answer 43

hydrogen

Question 44

how many allowed spin states does hydrogen have?

Answer 44

2

Question 45

what is Bo?

Answer 45

an external magnetic field

Question 46

in the presence of Bo, describe the 2 spin states of hydrogen

Answer 46

+1/2: the alpa spin state, lower in energy because flows with current of Bo -1/2: the beta spin state, higher in energy because flows against current of Bo

Question 47

what increases as Bo increases?

Answer 47

the energy gap (delta E) between alpha and beta spin states

Question 48

how do you calculate number of allowed spin states?

Answer 48

2I + 1

Question 49

what does the energy of radiofrequency match?

Answer 49

the change in energy between alpha and beta spin states

Question 50

what can the energy of radiofrequency do? what is this called?

Answer 50

spin flip! excite a nucleus from alpha to beta spin state

Question 51

in what state is the nucleus during/after a spin flip from radiofrequency energy?

Answer 51

resonating/in resonance

Question 52

define shielding

Answer 52

electrons create opposing magnetic field that partially cancels out the external magnetic field (Bo)

Question 53

what does shielding do to the felt Bo, the change in energy, and the radiofrequency?

Answer 53

1. decreases felt Bo by nucleus 2. decreased change in energy 3. decreases the radiofrequency energy required to excite a nucleus from alpha to beta spin state

Question 54

define deshielding

Answer 54

withdrawal of electron density via induction from electronegative atoms

Question 55

what does deshielding do to the felt Bo, the change in energy, and the radiofrequency?

Answer 55

1. increases the felt Bo 2. increases change in energy 3. increases the radiofrequency energy required to excite a nucleus from alpha to beta spin state

Question 56

what is anisotropy?

Answer 56

when the electrons in pi bonds create magnetic fields that either oppose (shield) or reinforce (deshield) the external magnetic field (Bo)

Question 57

name 3 functional groups where anisotropy can occur

Answer 57

1. alkenes 2 carbonyls 3. benzene rings

Question 58

what does anistropy explain?

Answer 58

the large deshielded chemical shift of benzenes and aldehydes

Question 59

what allows NMR differentiation?

Answer 59

the different electronic environments of each hydrogen nucleus in a compound

Question 60

what is splitting?

Answer 60

when NMR peaks appear anywhere from a singlet to a dectet, caused by the small magnetic field created by the neighboring hydrogen atoms that either shieldor deshield Bo

Question 61

what is integration?

Answer 61

the amount of hydrogen atoms that produce an NMR signal

Question 62

how to you determine splitting pattern?

Answer 62

N+1 (neighboring H atoms +1)

Question 63

what is the most common molecular weight of Cl in NMR?

Answer 63

35

Question 64

what is the most common molecular weight of Br in NMR?

Answer 64

79

Question 65

what does a quartet usually indicate structurally?

Answer 65

a H next to CH3

Question 66

what does 3H usually indicate structurally?

Answer 66

methyl (CH3)

Question 67

what does 2H usually indicate structurally?

Answer 67

CH2 group

Question 68

what does 6H usually indicate structurally?

Answer 68

2 identical CH3 groups