Section 1 Flashcards
(47 cards)
Benzene
If Kekule was right - bond length
Bonds would have different lengths
Benzene
Kekule wrong - bond length
X-ray diffraction showed that all carbon-carbon bonds are the same length
Benzene
The delocalised model
p-orbitals of all 6 carbons overlap to make pi-system
electron clouds above and below planar ring
Benzene
Hydrogenation evidence
Expect hydrogenation to be -360
But it was 208 - so far else exothermic than thought
Benzene is more stable
Benzene
Reaction
Electrophilic Substitution
Benzene
Bromination no
Kekule wrong because doesn’t readily undergo bromination
Benzene
Halogen carrier
Accepts a lone pair from a halogen atom on electrophile
As it’s pulled away polarisation increases
Benzene reacting with Halogen
Aluminium Chloride
Benzene
Friedel-Crafts alkylation
Haloalkane and reflux
Halogen carrier
Benzene
Friedel-Crafts alcylation
Reflux with acyl chloride
AlCl3
Nitration of Benzene
c. nitric and c. sulfuric acid
below 55
Benzene
Phenol more reactive
lone pairs on O overlap with delocalised ring, so they’re partially delocalised into the pi system
Increasing electron density so more likely to be attacked by electrophiles
Benzene
EDG direct substitutions where?
2,4,6
Benzene
EWG direct substitutions where?
3,5
Phenol
Bases
Weak acid so reacts with bases to form water and sodium phenoxide
Room temp
Primary alcohol to aldehyde
distill with acidified potassium dichromate
How to reduce ketones and aldehydes to alcohols
NaBH4
Reducing aldehyde and ketone mechanism
H- attacks carbon and double bond goes to O
O:- is left
O:- goes to H+ in dipole of water
Hydrogen Cyanide
Weak acid which dissociates to give H+ and CN-
Carbonyls and hydrogen cyanide
N=-C: attacks C
= goes to O making O:-
H+ goes to O:-
Hydrogen Cyanide dangers
toxic gas
solution of acidified cyanide is used
performed in fume cupboard
Test for aldehydes and ketones
2,4 - DNP - dissolved in methanol and concentrated sulphuric acid
Bright orange ppt - recrystallise and measure melting point and compare to known values
Test for aldehydes
Tollens’ reagent (silver nitrate in aq ammonia)
Silver mirror when tollens is reduced
COOH and reactive metal
Salt and hydrogen gas
