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Orgo II > C16: Aromatic Compounds > Flashcards

C16: Aromatic Compounds Flashcards

1
Q

benzene carbon-carbon bonds are _____ than typical C-C bonds, and ____ than typical ______

A

shorter
longer
C=C

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2
Q

bonds of a benzene ring are ______

A

all the same length

1.397 Angstroms

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3
Q

aromatic compounds are _____ containing some number of ____ bonds and having an unusually large ____

A

cyclic
conjugated double
resonance energy

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4
Q

cyclohexene + KMnO4 –>??

benzene + KMnO4 —>??

A 
cis diol (gylcol)
no reaction
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5
Q

cyclohexene + Br2 in CCl4 –>??

benzene + Br2 in CCL4 —>??

A

trans 1,2 bromocyclohexane

no reaction *** however adding FeBr3 catalyst will give bromocyclohexene

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6
Q

cyclohexene + H2, Pt –>??

benzene + H2, Pt —>??

A

cyclohexane

no reaction *** however adding heat and pressure will give cyclohexane

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7
Q

resonance energy

A

the difference between predicted and experimental energies

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8
Q

benzene resonance energy

A

-208 (151 kJ lower than predicted)

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9
Q

annulenes

A

cyclic hydrocarbons with alternating single and double bonds

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10
Q

cyclobutadiene
benzene
cyclooctatetraene
cyclodecapentaene

A

[4]annulene
[6]annulene
[8]annulene
[10]annulene

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11
Q

benzene first MO

A

donut, no nodes

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12
Q

benzene pi2 ___ pi3, both are ____ (bonding or antibonding)
pi2
pi3

A

= , bonding
vertical node splits in half
horizontal node splits in half

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13
Q

benzene pi4 ___ pi5, both are ____ (bonding or antibonding)
pi4
pi5

A

=, anti-bonding
vertical and horizontal nodes cut into quarters
diagonal x nodes

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14
Q

benzene pi5 ___ pi6

A

=/=
all antibonding
3 crisscrossing nodes

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15
Q

cyclobutadiene pi1___pi2
pi1
pi2

A

=/=
all bonding
vertical node, split in half

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16
Q

cyclobutadiene pi2___pi3
pi2
pi3

A

=
vertical node, split in half
horizontal node, split in half
both non-binding

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17
Q

cyclobutadiene pi3___pi4
pi3
pi4

A

=/=
horizontal node, split in half
horizontal and vertical node, split in quarters

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18
Q 
aromatic compounds:
1
2
3
4
A

1 structure is cyclic containing some # conjugated pi bonds
2 each atom in ring must have unhybridized p orbital
3 unhybridized p orbital must overlap/structure must be planar
4 delocalization of pi electron over entire ring must lower electronic energy

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19
Q

anti-aromatic compound:

A

meets one of three criteria of aromatic

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20
Q

benzene
cyclobutadiene
cyclohexa-1,3-diene

A

aromatic
antiaromatic
nonaromatic

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21
Q

Huckel’s Rule: to qualify as a aromatic or antiaromatic a ____ compound must have a ______ of _____ p orbitals usually in a ____ conformation

A

cyclic
continuous ring of overlapping
planar

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22
Q

Huckels Rule:
[1] How many pi electrons in the cyclic system?
= to 4N+2 –> ???
= to 4N –> ???

A

aromatic

antiaromatic

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23
Q

cyclooctatetraene

aromatic, anti-aromatic, nonaromatic, why?

A

nonaromatic, not planar

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24
Q

[12]annulene, [16]annulene, [20]annulene

aromatic, anti-aromatic, nonaromatic, why?

A

nonaromatic, nonplanar

25
Q

[10]annulene all-cis, two-trans, napthalene

aromatic, anti-aromatic, nonaromatic, why?

A

nonaromatic, nonaromatic, aromatic

nonplanar-ring strain

26
Q

[14]annulene, [18]annulene

aromatic, anti-aromatic, nonaromatic, why?

A

aromatic

27
Q

cyclopentadiene cation

aromatic, anti-aromatic, nonaromatic, why?

A

nonaromatic,

empty p orbital at (+)

28
Q

cyclopentadiene anion

aromatic, anti-aromatic, nonaromatic, why?

A

aromatic

two electrons in p orbital

29
Q

cyclopentene + ______ –> cyclopentadiene anion

A

-OC(CH3)3

potassium tert-butoxide

30
Q

cycloheptarienyl cation is also known as _____?

and is aromatic, anti-aromatic, nonaromatic, why?

A

tropylium ion,

aromatic

31
Q

cycloheptarienyl anion is also known as _____?

and is aromatic, anti-aromatic, nonaromatic, why?

A

tropylium ion,

antiaromatic

32
Q

formation of tropylium cation

A

cyclohep-2,4,6 trienenol + H+ +H20

33
Q

formation of tropylium anion

A

cycloheptriene + B:

34
Q

cyclooctatetraene + 2K —>????

A

aromatic dianion

35
Q

2pi electron aromatic

A

cyclopropenyl cation

36
Q

4pi electron antiaromatic

A

cyclobutadiene, cyclopropenyl anion, cyclopentadienyl cation

37
Q

6pi electron aromatic

A

benzene, cyclopentadienyl anion, cycloheptatrienyl cation

38
Q

heterocyclic 6pi electron aromatic

A

pyridine (benzene with N in place of C, 3 double bonds still)
pyrrole (cyclopentane with NH in place of C)
furan (cyclopentane with O in place of C)

39
Q

8pi electron antiaromatic

A

cyclooctatetraene, cycloheptatrienyl anion, cyclononatetraenyl, pentalene

40
Q

10pi electron aromatic

A

napthalene, azulene, cyclononatetraenyl anion, cyclooctatetraenyl dianion

41
Q

heterocylic 10 pi aromatic

A

indole (benzene + pyrrole)

quinoline (benzene + pyridine)

42
Q

12pi electron antiaromatic

A

[12]annulene, heptalene

43
Q

pyrrole

A

aromatic 5 membered ring wiht one nitrogen atom and 2 double bonds

44
Q

pyrimidine

A

two basic N in a six membered ring, aromatic

45
Q

imidazole

A

one basic and one protonated N in an aromatic 5 membered ring

46
Q

purine

A

an imidazole ring fused to a pyrimidine ring

47
Q

furan

A

aromatic five membered ring with oxygen instead of nitrogen in place of carbon

48
Q

thiophene

A

furan with sulfur instead of oxygen

49
Q

as the number of fused aromatic rings ____ the resonance energy per ring _____ and the compound becomes _____ reactive

A

increase, decrease, more

50
Q

fused rings often attacked at __ and __ position

A

9- and 10- position

51
Q

_____ of ____ extends through the crystal as ____ molecule, ____ carry current

A

lattice, diamond, giant, unable to

52
Q

graphite is _____ stable than diamond and a _____ conductor along the ____ but not _____

A

more, parallel to the layers perpendicular to the layers

53
Q

aromatic compounds are identified in IR by

A

1600cm-1 stretch C=C

54
Q

aromatic compounds are identified in HNMR by

A

delta of 7 or 8

55
Q

aromatic compounds are identified in C13NMR by

A

delta of 120 to 150

56
Q

mass spec of benzene usually splits with a m/z of

A

91 from benzyl cation

alkyl benzene frequently give tropylium ion at m/z of 91

57
Q

UV of aromatic
1
2
3

A

1 lamda = 184 (undetectable)
2 lamda = 204 moderate band
3 lamda = 254 low-intensity

58
Q

adding groups _____ lamda absorption wavelength

A

increases

Orgo II (8 decks)

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