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From Flashcardlet > *Organic Test 2 > Flashcards

*Organic Test 2 Flashcards

1
Q

How do you know whether the ring or the chain is the parent?

A

The parents is the ring unless the side chain is larger or there is a functional group present in the side chain

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2
Q

How do you name the parent?

A

The number of carbons in the ring or the number of carbons in the longest chain

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3
Q

How do you name substituents?

A

Point of attachment is carbon 1, and continue so that the second substituent has the lowest number possible

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4
Q

How do you name substituents if two alkyl groups could have the same number?

A

Number them alphabetically (1-ethyl-2-methyl)

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5
Q

How does ring size influence flexibility?

A

The larger rings have more flexibility (C3-C7 are very restricted)

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6
Q

What are the two faces of a ring?

A

Cis and trans

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7
Q

What is a stereoisomer?

A

Compound that has its atoms connected in the same order but differs in its 3D orientation

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8
Q

What is stereochemistry?

A

The 3D aspects of chemical structure and reactivity

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9
Q

What is a constitutional isomer?

A

Different connections between atoms

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10
Q

What is cis?

A

Same side

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11
Q

What is trans?

A

Opposing sides

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12
Q

What is angle strain?

A

The strain induced in a molecule when bond angles are forced to deviate from the ideal 109.5 degrees tetrahedral angle

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13
Q

How do you measure the strain in a compound?

A

The measure of total energy of a compound - the energy of a strain free reference compound
(The difference represents the amount of extra energy due to strain)

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14
Q

What is the heat of combustion?

A

The amount of heat released when a compound burns completely with oxygen

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15
Q

The more strain, the more/less energy released on combustion

A

More strain, more energy released

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16
Q

How do cycloalkanes arrange themselves to reduce angle strain?

A

Most are puckered 3D formations that allow bond angles to be nearly tetrahedral

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17
Q

What are the two important factors influencing the amount of energy strain in a compound?

A

Torsional strain from H-H eclipse
Steric strain from repulsion between non bonded atoms that approach too closely
(Angle strain also to a certain extent)

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18
Q

Which cycloalkane is the most strained?

A

Cyclopropane because it has 60 degrees bond angles and all of its Hs are eclipsed

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19
Q

What does it mean that cyclopropane has bent bonds? What does this result in?

A

Cannot overlap sigma orbitals head to head, so they overlap at a slight angle, resulting in weaker and more reactive bonds

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20
Q

What is the conformation of hexane called (2)?

A

Chair or boat conformation

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21
Q

What is the conformation of pentane called?

A

Envelope conformation

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22
Q

What kind of strain does the chair conformation have?

A

If all C-Hs, no strain because there is no angle or torsional strain, C-H bonds are staggered, and bond angles are at 109.5

(Steric strain if other groups are attached)

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23
Q

Which is higher energy, chair or boat?

A

Boat, because it has steric and torsional strain - it is only adopted under special circumstances

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24
Q

What are the two positions for substituents on a ring?

A

Axial and equatorial

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25
Q

What is axial?

A

Perpendicular to the ring (or parallel to the axis)

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26
Q

What is equatorial?

A

In the rough plane of the ring

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27
Q

How many A and E Hs do each C have in a cyclohexane?

A

1 A and 1 E

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28
Q

How many A and E Hs do each face have in a cyclohexane?

A

3 A and 3 E on each face

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29
Q

What is the chair flip?

A

The four middle Cs are kept in place while the two end Cs are flipped in opposite directions

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30
Q

Does cyclohexane have isomers?

A

No, it rapidly changes with ring flip so we see a hybrid

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31
Q

Which is more stable, a group in axial or equatorial?

A

Equatorial

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32
Q

Why is axial less stable?

A

Because the group has steric energy in the axial position

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33
Q

What is the equation that calculates the percentage of two isomers at equilibrium? What do we use instead?

A

Delta E = -RTlnK
(E = difference between isomers, R = gas constant, T = temp in Kelvin, K = equilibrium constant)
We use the graph instead

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34
Q

How do we use the graph?

A

We calculate the difference in energy between the two isomers and use this value to find the percent of that isomer

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35
Q

What is the energy difference between two conformations caused by?

A

1,3 diaxial interactions

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36
Q

What is the strain for 1,3 diaxial interaction of CH3?

A

7.6 kJ/mol

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37
Q

What is decalin?

A

2 cyclohexane rings fused together

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38
Q

What are bridgehead carbons?

A

The carbons along which two rings are fused

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39
Q

What is an enantiomer?

A

Molecules that are non superimposable mirror images

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40
Q

What is bonded to a carbon to make it an enantiomer?

A

4 different groups

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41
Q

What are diastereomers?

A

Stereoisomers that aren’t enatiomers

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42
Q

What is the term for a carbon with four different substituents?

A

Chiral center

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43
Q

A chiral molecule has/does not have a plane of symmetry

A

A chiral molecule does not have symmetry

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44
Q

How are enantiomers similar and different?

A

They have almost all the same properties (solubility, BP, MP, IR, NMR, mass spec, etc) but they have different optical activity and biological activity

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45
Q

What is a polarimeter?

A

A light wave oscillating in a single plane passes through the molecule, and if the molecule is optically active, it will bend the light

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46
Q

What is it called when optically active molecules rotate polarized light to the left?

A

Levorotatory

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47
Q

What is it called when optically active molecules rotate polarized light to the right?

A

Dextrorotatory

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48
Q

What is the formula for specific rotation?

A

[alpha]D = alpha/l x c

[alpha]D = specific rotation
alpha = observed rotation in degrees
l = length in dm
c = concentration in g/ml
49
Q

How many cm in a dm?

A

10 cm = 1 dm

50
Q

How do enantiomer’s specific rotation compare?

A

They are the same value except one is positive and one is negative

51
Q

What is the value of alpha if the molecule is optically inactive?

A

0 degrees

52
Q

What is the value of alpha of a racemic mixture?

A

0 degrees, because the dextro and levo cancel one another

53
Q

What is a racemic mixture?

A

A 50:50 mixture of the two enantiomers

54
Q

What is the Cahn Ingold Prelog system?

A

Assigning priority of the four groups attached at the chiral center according to atomic number
(Higher atomic #, first priority)

55
Q

How do you orient a chiral molecule so that you can determine R or S?

A

So that the lowest priority is facing away from you

56
Q

What is R orientation?

A

123 clockwise

57
Q

What is S orientation?

A

123 counterclockwise

58
Q

What is formula for the maximum number of stereoisomers?

A

2^n

59
Q

Which are enantiomers and which are diastereomers of RR?

A 
Enantiomer = SS
Diastereomers = RS and SR
60
Q

What are the three factors qualifying a meso form?

A
  1. The two chiral centers are made of the same four groups
  2. The molecule has an SR absolute configuration
  3. The molecule has an internal plane of symmetry
61
Q

How do double bonds count in the Cahn Ingold Prelog system?

A

C=O is equivalent to C bonded to 2 O

62
Q

Is the sign of optical rotation related to the RS configuration?

A

No

63
Q

Enantiomers have opposite configurations at how many chiral centers?

A

All

64
Q

Diastereomers have opposite configurations at how many chiral centers?

A

Some

65
Q

What is an epimer?

A

Two diastereomers differ at only one chirality center but are the same at all the others

66
Q

What is the definition of a mess compound?

A

Compounds that are a chiral because they are symmetrical but have chirality centers

67
Q

What is the most common method of resolution for a racemic mixture?

A

Using an acid base reaction - Carboxylic acid and an amine

68
Q

What results when NH2 is added to the racemic mixture?

A

2 diasteromeric salts are produced (2 ionic compounds)
They now have different properties - different solubilities and BP so that they can be filtrated or evaporated into separation

69
Q

What are the two limitations to resolution of a racemic mixture using acid-base reactions?

A

The enantiomers need to have a carboxylic acid as one of their groups
The amine needs to be a pure enantiomer itself

70
Q

What atoms can be chiral other than carbon?

A

N, S, P

71
Q

How does N configure into a tetrahedral?

A

The lone pair pulls up on the molecule into a tetrahedral

72
Q

What priority is the lone pair assigned?

A

0

73
Q

What is pyramidal inversion?

A

If the sp2 rehybridizes with the top p orbital, it returns to the tetrahedral with a lone pair on top.
If the sp2 rehybridizes with the bottom p orbital, it continues to the tetrahedral with a lone pair on the bottom.
The molecule constantly shifts like this back and forth

74
Q

How do we stop pyramidal inversion?

A

The only way is to bond the lone pair to something

75
Q

What is prochirality?

A

The molecule can be converted from a chiral to chiral in a single chemical step

76
Q

What are the two faces of a trigonal planar molecule?

A

Re face and Si face

77
Q

What is the Re face?

A

123 clockwise

78
Q

What is the Si face?

A

123 counterclockwise

79
Q

How do you determine Re or Si face?

A

Number the groups with priorities like usual, with the potential H in back

80
Q

How do you determine Re or Si face if there are 2 H?

A

Replace one H with deuterium. D becomes priority 3 and H is priority 4.

81
Q

What are the two kinds of isomers?

A

Constitutional and stereoisomers

82
Q

What are the two kinds of stereoisomers?

A

Enantiomers and diastereomers

83
Q

What are the two kinds of diastereomers?

A

Configurational and cis-trans

84
Q

Can we isolate N enantiomers?

A

Not usually, since they interconvert so quickly, but P and S interconvert more slowly, so it is possible

85
Q

Why are enantiomers biologically different?

A

Because receptors are chiral, so only one enantiomer of a chiral substrate can bind

86
Q

What is the term for the area that receptors create when they are chiral?

A

Chiral environment

87
Q

What is an addition reaction?

A

A + B –> C

88
Q

What is an elimination reaction?

A

C –> D + E

89
Q

What is a substitution reaction?

A

A-B + C-D –> A-D + B-C

90
Q

What is a rearrangement reaction?

A

A –> A^1

Like constitutional isomers

91
Q

What is another term for mechanism?

A

Pushing arrows

92
Q

What is a reaction used for?

A

Used to learn how a reaction works, instead of memorizing reagents and products

93
Q

What does a double headed arrow represent?

A

Movement of 2 electrons

94
Q

What does a single headed arrow represent?

A

Movement of 1 electron

95
Q

What is homolytic cleavage?

A

An even break, where each product receives one of the two electrons, resulting in radicals

96
Q

What is heterolytic cleavage?

A

An uneven break where one product receives 2 electrons and one receives none (Polar reaction)

97
Q

What is an electrophile?

A

Electron loving, attracted to electrons

98
Q

What is a nucleophile?

A

Nucleus loving, attracted to the protons of the nucleus

99
Q

What is the charge of an electrophile?

A

Usually positive, or neutral

100
Q

What is the charge of a nucleophiles?

A

Usually negative, or neutral

101
Q

Is B an electrophile or nucleophile?

A

Electrophile because it can take on more electrons

102
Q

What are some things to look for in nucleophiles?

A

Negative formal charge
Lone pairs
Pi bonds
Partial negative

103
Q

What are some things to look for in electrophiles?

A

Positive formal charge
Electron deficient
Partial positive

104
Q

What are the four rules for writing reactions?

A
  1. Electrons move from nucleophiles to electrophiles
  2. Nucleophiles can be negative or neutral
  3. Electrophiles can be positive or neutral
  4. Follow the octet rule
105
Q

What is the name of the reaction that we need to know the mechanism for?

A

Electrophilic addition to alkenes

106
Q

Which species is attracted to which?

A

Nucleophiles are attracted to electrophiles

107
Q

What is K?

A

Equilibrium constant

108
Q

What is the formula for K?

A

[products]/[reactants]

109
Q

What is delta G?

A

Change in Gibbs free energy

110
Q

What is the equation for delta G?

A

Delta G = -RTlnK

111
Q

What does a negative delta G represent?

A

Spontaneous reaction

112
Q

What does a positive delta G represent?

A

Nonspontaneous reaction

113
Q

What does a negative delta H represent?

A

Exothermic reaction

114
Q

What does a positive delta H represent?

A

Endothermic reaction

115
Q

What is delta H?

A

Enthalpy - Heat content

116
Q

What is delta S?

A

Entropy - Amount of disorder or randomness in the system

117
Q

What is the equation with all three deltas?

A

Delta G = Delta H - TDeltaS

118
Q

What can we assume about the relationship between Delta G and H? What is the stipulation?

A

The values are about the same, as long as |delta H|>40 kJ

119
Q

What does the table of bond dissociation energies show?

A

The energy it takes to break a bond

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