Explainations of Benzene and Phenol

This is to help with the 3 mark questions like, "explain how the structure of Benzene relates to it's reactions", etc.

DC= Degrees Celcius,

RTP= Room Temperature + Pressure,

STP= Standard Temperature + Pressure,

EC=Enthalpy Change,

HC= HydroCarbon,

e- = electron(s)

LP=Lone Pair (of e-).

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  • Created by: Arianne
  • Created on: 08-01-13 22:32
3 forms of evidence against Kekule structure of Benzene.
X-Ray crystallography, low reactivity with Br2, Heats of hydrogenation.
1 of 8
How does X-Ray Crystallography show Kekule structure to be wrong?
C=C bond length shorter than C-C, however in Benzene all bond lengths (and C-C-C bond angles) the same (somewhere between C=C and C-C).
2 of 8
ow does it's low reactivity with Br2 show Kekule structure to be wrong?
C=C bonds react readily with Br2 at RTP, Benzene does not (requires a halogen carrier) therefore contains no C=C.
3 of 8
How does heats of hydrogenation show Kekule structure to be wrong?
When C=C is hydrogenates, enthalpy change = -120Kj/mol. In Kekule, 3x C=C, so expected EC= -360Kj/mol. EC in Benzene is -208Kj/mol, so is 152kj/mol more stable than Kekule structure suggests. (152Kj/mol) is known as delocalisation energy.
4 of 8
Describe C-C bonding in Benzene.
Each C has 4 outer shell e-. 3 are in sigma bonds. E- in p-orbital overlaps with neighbouring e-, forming a ring of e- density above and below the plane of the ring. System of Pi bonds, which are delocalised over the 6 Cs.
5 of 8
Why does Benzene react slower with Br2 than Phenol?
LP of e- in phenol is partially delocalised into the plane of the ring so ring becomes overall more negative and can induce a dipole in Br2, and also makes it more attractive to electrophiles (eg, NO2+)
6 of 8
S&C Why is Methylbenzene less reactive than Benzene?
Positive inductive effect removes e- PARTIALLY from the ring structure, making it less negative and therefore less able to induce a dipole in Br2 and also less attractive to electrophiles.
7 of 8
Uses of phenols?
Alkylphenols in detergents, Chlorophenols in disinfectants, Bisphenol as paint resin.
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Other cards in this set

Card 2

Front

How does X-Ray Crystallography show Kekule structure to be wrong?

Back

C=C bond length shorter than C-C, however in Benzene all bond lengths (and C-C-C bond angles) the same (somewhere between C=C and C-C).

Card 3

Front

ow does it's low reactivity with Br2 show Kekule structure to be wrong?

Back

Preview of the front of card 3

Card 4

Front

How does heats of hydrogenation show Kekule structure to be wrong?

Back

Preview of the front of card 4

Card 5

Front

Describe C-C bonding in Benzene.

Back

Preview of the front of card 5
View more cards

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