Aromaticity

6-pi electrons in the cyclic planar system, as one lone electron pair of S is not on the sp2 orbital but on the unhybridized p orbital along the ring

EXTRA D-I-Y PROBLEMS

EAS: REACTIONS of Aromatics

BROMINATION/CHLORINATION

BROMINATION/CHLORINATION

NITRATION

NITRATION

SULFONATION

SULFONATION

FRIEDEL-CRAFTS ALKYLATION

FRIEDEL-CRAFTS ALKYLATION

FRIEDEL-CRAFTS ALKYLATION LIMITATIONS!!!!

FRIEDEL-CRAFTS ALKYLATION Another limitation is that the reaction is hard to control and alkylates more than once. CARBOCATION rearrangement happens here too! This can be avoided by a 2-step synthesis starting from FRIEDEL-CRAFTS ACYLATION

FR-CR ACYLALTION

FR-CR ACYLALTION

FR-CR ACYLALTION By using REDUCTION via H2, Pd / Ethanol after, we can make it an alkyl group

FR-CR ACYLALTION We ALSO AVOID LOSING CONTROL OF ACYLATION, UNLINK IN ALKYLATION WHERE IT ADDS MULTIPLE TIMES. IT ONLY ADDS ONCE, PER REACTION

REDUCTION OF NO2/C=O GROUP NOTE: ONLY THE C=O NEXT TO THE AROMATIC RING CAN BE REDUCED TO THE CH2!!!!!

REDUCTION OF NO2/C=O GROUP NOTE: ONLY THE C=O NEXT TO THE AROMATIC RING CAN BE REDUCED TO THE CH2!!!!!

REDUCTION OF NO2 alternative

REDUCTION OF AROMATICS Rh/C catalyst Vs. EXTREME PRESSURES!

OXIDATION OF SIDE CHAINS DOUBLE BONDS ARE NOT CLEAVED. SIDE CHAINS ARE CLEAVED, LEAVING A –COOH on the AROMATIC, BUT ONLY WORKS WHEN THERE IS A HYDROGEN ATTACHED TO THE FIRST CARBON.

OXIDATION OF SIDE CHAINS DOUBLE BONDS ARE NOT CLEAVED. SIDE CHAINS ARE CLEAVED, LEAVING A –COOH on the AROMATIC, BUT ONLY WORKS WHEN THERE IS A HYDROGEN ATTACHED TO THE FIRST CARBON.

ACTIVATING VS. DEACTIVATING: supplying more electrons to a (+) carbocation = stabilizing!

2 EFFECTS IMPORTANT: INDUCTIVE: sharing/withdrawing electrons via SIGMA BOND / single bond, electronegativity effects RESONANCE: sharing/withdrawing electrons via PI BONDS / DOUBLE BONDS. These two add together. Net Effect determines if Activating/Deactivating

ELECTRONEGATIVE GROUPS CAN PULL ELECTRONS TOWARDS THEM, DEACTIVATING THE RING… ALKYL GROUPS STRONGLY DONATE, ACTIVATING IT.

RESONANCE WITHDRAWING = EVEN MORE DEACTIVATION AGAIN USUALLY WITH ELECTRONEGATIVE SPECIES LIKE ≡N/=O

RESONANCE DONATING, ELECTRON-RICH –O— or –NR3 or –X, has lots of lone pairs to share

PUTTING TOGETHER BOTH EFFECTS…

PUTTING TOGETHER BOTH EFFECTS… We can also see how/why these groups tend to direct either to an Ortho/Para or a Meta position through these effects.

CARBOCATION STABILIZED BY INCREASING BRANCHING!

CARBOCATION IS AVOIDED!!

CARBOCATION IS AVOIDED!!

CARBOCATION WHERE ELECTRONS ARE WITHDRAWN = BIG NO NO CARBOCATION WHERE ELECTRONS ARE WITHDRAWN = BIG NO NO!!! WE WANT TO GIVE ELECTRONS TO THE (+) NOT TAKE FROM IT EVEN MORE!

1. IF BOTH GROUPS ALREADY DIRECT THE SAME WAY.. YAY.

2. IF THEY DON’T, you need to RANK!

3. AND TRY TO AVOID CROWDS/ HINDERED SUBSTITUTIONS!

So… WE PUT EVERYTHING TOGETHER So… WE PUT EVERYTHING TOGETHER. WE CAN NOW DEVISE SYNTHETIC ROUTES = ways to make a more complex molecule.

Synthesize this from BENZENE, using the reactions you know…

1. What possible last steps are there?

2. From that, how will you make the intermediate you need?

3. Then from Benzene, make your routes go forward after solving it backwards.

PRACTICE!