Notes for Exam 1

Question 1

Conformational isomers (conformers)

Answer 1

Same molecular formula
Same connectivity
Different spatial arrangements of atoms
Interconversion occurs by rotation around single bonds

Question 2

Primary carbons

Answer 2

Are bonded to 1 other carbon

Question 3

Secondary carbons

Answer 3

Are bonded to 2 other carbons

Question 4

Tertiary carbons

Answer 4

Are bonded to 3 other carbons

Question 5

Why are eclipsed conformations more strained than staggered conformations?

Answer 5

It’s due to torsional strain

Question 6

How much energy is stored in each gauche position?

Answer 6

~0.9 kcal/mol

Question 7

How do you mathematically know which conformer is favored?

Answer 7

Use their energy differences

deltaE = E(products) - E(reactants)

If deltaE < 0, products favored
If deltaE > 0, reactants favored

Question 8

If the products are favored, what should a reactions deltaE be?

Answer 8

Less than 0

Question 9

If the reactants are favored, what should a reactions deltaE be?

Answer 9

Greater than 0

Question 10

Cyclopropane: H-position

Answer 10

Eclipsed

Question 11

What kinds of strain does cyclopropane have?

Answer 11

Angle and torsional, and therefore ring

Question 12

How much energy is stored in cyclopropane?

Answer 12

27.7 kcal/mol

Question 13

Cyclobutane: H-positions

Answer 13

If planar, H’s are eclipsed

If puckered, H’s are not quite eclipsed

Puckered form somewhat relieves the ring strain

Question 14

Cyclopentane: H-positions

Answer 14

If planar, H’s are eclipsed

If envelope, H’s are not eclipsed

Question 15

Cyclopentane: actual bond angles

Answer 15

If planar, 108

If envelope, 105

Question 16

Cyclohexane: H-positions

Answer 16

If planar, H’s are eclipsed

If chair, H’s are staggered

Question 17

Cyclohexane: actual bond angles

Answer 17

If planar, 120

If chair, 110

Question 18

What happens to strain as substituent size increases?

Answer 18

Strain will increase

Question 19

Stereoisomers

Answer 19

Same molecular formula
Same connectivity
Different spatial orientations
CANNOT be interconverted by single bond rotations

Question 20

Will the following two substituents have gauche interactions with each other?

Axial and equatorial

Answer 20

Yes

Question 21

Will the following two substituents have gauche interactions with each other?

Equatorial and equatorial

Answer 21

Yes

Question 22

Will the following two substituents have gauche interactions with each other?

Equatorial and axial

Answer 22

Yes

Question 23

Will the following two substituents have gauche interactions with each other?

Axial and axial

Answer 23

No

Question 24

If two substituents are separated by a ~60 degree angle, will they have gauche interactions with each other?

Answer 24

Yes

Question 25

If two substituents are separated by a ~180 degree angle, will they have gauche interactions with each other?

Answer 25

No, they are in the anti position

Question 26

What happens to an alkane's boiling point as the number of carbons in its chain increases?

Answer 26

Boiling point increases

Question 27

What happens to an alkane's boiling point as branching within the molecule increases?

Answer 27

Boiling point decreases

Question 28

Enantiomers

Answer 28

A pair of non-superimposable (chiral) molecules

Question 29

Compare chiral vs achiral objects

Answer 29

Achiral objects ARE superimposable onto their mirror images and have a plane of symmetry Chiral objects are NOT superimposable onto their mirror images

Question 30

Achiral objects

Answer 30

Are superimposable onto their mirror images Have a plane of symmetry

Question 31

Steroeocenter

Answer 31

An atom in a molecule at which the interchange of 2 groups produces a stereoisomer

Question 32

R/S System: which has more priority? OH, CH3, NH2

Answer 32

OH = 1 NH2 = 2 CH3 = 3

Question 33

R/S System: which has more priority? Methyl group, ethyl group

Answer 33

Eth = 1 Me = 2

Question 34

R/S System: which has more priority? Eth, NH2, Me

Answer 34

NH2 = 1 Eth = 2 Me = 3

Question 35

R/S System: clockwise substituents

Answer 35

R

Question 36

R/S System: counterclockwise substituents

Answer 36

S

Question 37

How many stereoisomers will a molecule have?

Answer 37

Depends on the number of stereocenters present (n) Formula is 2^n So a molecule with 1 stereocenter has 2 possible stereoisomers

Question 38

Which has a larger dipole, O=N or O=S?

Answer 38

O=S

Question 39

Acid-base reactions will favor the protonation of the...

Answer 39

...weaker acid Side with the larger pKa is favored

Question 40

To reduce steric strain in a chair conformer, where should the largest substituent be placed?

Answer 40

In the equatorial position

Question 41

How are Ka and pKa mathematically related?

Answer 41

Inversely Low Ka --> high pKa High pKa --> low Ka

Question 42

Are carboxylic acids strong acids or weak acids?

Answer 42

Weak acids

Question 43

Are amines strong bases or weak bases?

Answer 43

Weak bases

Question 44

Which proton is more acidic? OH or SH

Answer 44

SH

Question 45

Which proton is LESS acidic? OH or SH

Answer 45

OH

Question 46

Rank the following protons from LEAST to MOST acidic FH, BrH, ClH, IH

Answer 46

I, Br, Cl, F

Question 47

Rank the following protons from MOST to LEAST acidic FH, BrH, ClH, IH

Answer 47

F, Cl, Br, I

Question 48

If a molecule forms a very unstable conjugate base when deprotonated, will its pKa be low or high?

Answer 48

High

Question 49

If a molecule forms a very stable conjugate base when protonated, will its pKa be low or high?

Answer 49

Low

Question 50

When justifying why a resonance structure is more stable, what should you include?

Answer 50

The number of covalent bonds Location of the negative charge Number of complete octets