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OCHEM > Chapter 7 > Flashcards

Chapter 7 Flashcards

1
Q

alkenes are hydrocarbons with _______ bonded carbons. This is also called _______

A

double
olefin

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2
Q

Sigma bonds around the double bonded C’s are _______ hybridized

A

sp2

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3
Q

Unhybridized p orbitals with ___ electron each will overlap, forming the _______ bond. This overlap requires the 2 ends of the molecule to be coplanar

A

1
pi

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4
Q

Sp2 hybrid orbitals have _______ s character than sp3 hybrid orbitals. This results in _______ bonds

A

more
shorter (S is closer than P orbital; 2 bonds draw atoms closer)

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5
Q

Rotation around double bonded C is _______ without breaking the pi bond. Therefore, Cis and Trans isomers _______ be interconverted

A

impossible
cannot

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6
Q

Alkanes are called saturated hydrocarbons because they contain only _______ bonds

A

single (sigma)

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7
Q

alkenes are _______ because they are able to add Hs in the presence of a catalyst

A

unsaturated

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8
Q

unsaturation values are _______
double bond: _______
Ring: _______
triple bond: _______

A

additive
1
1
2

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9
Q

What is the formula for calculating elements of unsaturation?

A

((2n+2) - #H - #X + #N) / 2
n= carbons
H= hydrogens
X= halogens
N= Nitrogen
O and S have no effect

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10
Q

Nomenclature of alkenes
1) longest carbon chain that contains _______
2) Lowest # to _______
3) When numbering is equal for double bonds, look at _______ then use _______
4) If double bonds are positioned in C1 and C2 of a ring, assume they are _______
5) finally, add geometric isomerism prefix:

A

1) double bonds
2) double bonds
3) substituents, alphabetization
4) cis
5) cis/trans and E/Z

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11
Q

What are the 4 double bond containing substituents?

A

1) methylene
2) vinyl
3) allyl
4) isopropenyl

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12
Q

Cis trans isomerism is not possible if one of the double bonded C’s has _______ groups

A

identical

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13
Q

You only use E/Z nomenclature when you have ___ or ____ different substituents

A

3 (trisubstituted)
4 (tetrasubstituted)

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14
Q

Use Cahn-Ingold Prelog rules when assigning priority for _______ nomenclature

A

E/Z

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15
Q

When naming alkenes, E/Z are placed in _______ at the front of the name. It is also accompanied by a __ indicating the position of the alkene in the molecule

A

parentheses
#

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16
Q

In E/Z nomenclature __ is where high priority are going to be the same __ is where high priority are across

A

Z
E

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17
Q

The physical properties of alkenes are _______ to those of alkanes
- _______ dense than water
- branched alkenes have _______ bp
- slightly _______
- Cis alkenes have ________ bp than trans alkenes

A

similar
- less
- lower
- polar
- higher

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18
Q

The chemical properties of alkenes are _______ than those of alkanes
- more reactive because of the _______ bond electrons

A

different
pi

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19
Q

Combustion of an alkene and hydrogenation of an alkene can provide valuable data to the _______of the double-bonded C

A

Stability

20
Q

More substituted double bonds are usually _______ stable

A

more

21
Q

_______: alkenes with more highly substituted double bonds are usually more stable

A

zaitsev’s rules

22
Q

trans isomers are generally _______ stable than the corresponding cis isomer

A

more

23
Q

Alkenes with more alkyl groups are more stable because the alkyl groups are _______, which help to stabalize the pi-system (double bond)

A

EDG’s

24
Q

Rings that are __-membered or larger can easily accommodate double bonds and these cycloalkenes react much like straight chain alkanes

A

5

25
Q

Cis isomer is _______ stable than trans in small cycloalkanes

A

more

26
Q

Rings must have at least __ carbons to form a stable trans double bond. The larger the ring the more stable the trans will be

A

8

27
Q

Bredt’s Rule: a bridged bicyclic compound can’t have a double bond at a bridgehead position unless one of the rings contains at least __ carbon atoms

A

8

28
Q

Conjugated systems require __ or more p-orbitals in a row which leads to enhanced stability of the system

A

3

29
Q

All elimination reactions produce _______ bonds. The H+ is grabbed from the C that is adjacent to the ________.

A

double
LG

30
Q

Elimination reactions are also known as _______ reactions

A

dehydrohalogenation

31
Q

E1 will always be a minor product of Sn1 reactions, which will reduce the % yield of a reaction. This minor product will be ignored except for a very specialized case: dehydration of _______ with no _______ available

A

dehydration of alcohols with no nucleophile available

32
Q

All E2 reactions are _______
- do they have any intermediates?

A

concerted
no intermediates

33
Q

What is the rate law for E2 reactions?

A

rate = k [R-LG] [base]

34
Q

What is the order of reactivity of alkyl halides for E2 reactions?

A

3° > 2° > 1°
- reflects stablility of double bonds

35
Q

Most E2 reactions follow _______: the more highly substituted alkene is the major product. What are the 2 exceptions?

A

Zaitsev’s rules
1) Hofmann’s rule
2) Conjugation

36
Q

Hofmann’s rule: when a base is _______ the _______ highly substituted alkene is the major product

A

big and bulky
less

37
Q

What are the 4 big bases that follow Hofmann’s rule?

A

1) tert-butoxide (KOTBu)
2) LDA (has negative charge)
3) Et3N
4) 2,6-dimethylpyridine

38
Q

Conjugation: if the possibility of forming a conjugated product exists, it will _______ be the major product

A

always
trumps Hofmann’s rule and Zaitsev’s rule

39
Q

The E2 reaction follows a concerted mechanism, which requires a specific geometric arrangement so that the orbitals of the bonds _______ (LG) can overlap with those being _______ (double bond)

A

broken
formed

40
Q

What are the 2 coplanar arrangments for the reactions of E2 reactions?

A

1) anti-coplanar (low E)
2) syn-coplanar (high E)

41
Q

Which coplanar arrangement is favored in most E2 reactions?

A

anti-coplanar

42
Q

syn-coplanar reactions are only favored in _______ systems

A

restricted (rings)

43
Q

anti-coplanar elimination: E2 is a _______ reaction

A

stereospecific
(wedges on top, dashes on bottom)

44
Q

For E2 reactions to work in cyclohexane rings, the H and the LG must be _______ to form the double bond.

A

coplanar
- Only axial H can be used when LG is also axial

45
Q

2 axial bonds are trans to each other are called _______

A

trans-diaxial

46
Q

If there are no trans-diaxial H and LG then _______ occurs

A

no reaction

OCHEM (9 decks)

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