27 - Aromatic Chemistry Flashcards

1
Q

What are arenes?

A

Hydrocarbons based on benzene.

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2
Q

What was the anomaly with benzenes reactions?

A

Despite being unsaturated it does not readily undergo addition reactions.

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3
Q

What was the anomaly with benzenes bond lengths?

A

All of its bond lengths were equal, when they should have been different sizes, due to C=C bonds being shorter than C-C bonds.

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4
Q

What was the anomaly with benzenes enthalpy?

A

The enthalpy change for the hydrogenation of cyclohexane is -120, so the expected enthalpy for benzene is -360, however the actual enthalpy is -208 so benzene is more stable than expected.

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5
Q

Explain the structure of benzene.

A

One electron of each carbon atom is in a p-orbital, all p-orbitals overlap, creating a delocalised pi system and forming a region of electron density above and below the ring, making it extremely stable.

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6
Q

What is the shape and bond angles of benzene?

A

Trigonal planar
120

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7
Q

What is the melting and boiling point of benzene like?

A

Its boiling point is similar to hexane but its melting point is much higher than hexane, as the flat molecules pack together well in the solid state.

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8
Q

What is the solubility of benzene like?

A

Only mixes with other hydrocarbons and non-polar solvents as its non-polar.(Not soluble in water).

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9
Q

What reaction does benzene undergo and why?

A

Electrophilic substitution
The area of high electron density means they are susceptible to attack by electrophiles, but the ring is very stable so the ring remains intact in most reactions.

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10
Q

What is an electrophile?

A

Electron pair acceptor

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11
Q

What are the reagents of nitration of benzene and their reactions?

A

conc. nitric acid + conc. sulphuric acid
H2SO4 + HNO3 –> H2NO3+ + HSO4-
H2NO3+ –> NO2+ + H2O

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12
Q

Why does the sulfuric acid in the nitration of benzene act as a catalyst?

A

As it can be regenerated with the H+ product formed.

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13
Q

What is the name of the mechanism for the nitration of benzene?

A

Electrophilic substitution

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14
Q

What are the conditions of the nitration of benzene?

A

Reflux at 55 degrees

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15
Q

What is acylation?

A

Substituting an acyl group.

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16
Q

What are the reagents for Friedel-Crafts acylation of benzene?

A

An acyl chloride + anhydrous aluminium chloride (catalyst)

17
Q

What are the conditions of the acylation of benzene?

A

Reflux at 50 degrees
Dry inert solvent, as anhydrous AlCl3 is highly reactive in water and the acyl chloride will form back into a carboxylic acid.

18
Q

What are the products of the acylation of benzene?

A

Aldehyde or ketone

19
Q

What is the electrophile for the acylation of benzene?

A

RCO+

20
Q

What is the electrophile for the nitration of benzene?

A

NO2+

21
Q

How do electron releasing groups affect further substitution of benzene?

A

They make the ring more susceptible to further electrophilic substitution as the electron density of the ring increases.

22
Q

What are examples of electron releasing groups?

A

CH3, OCH3, OH, NH2

23
Q

To which positions will further substitutions go if an electron releasing group is attached to the benzene ring?

A

2, 4, 6

24
Q

How do electron withdrawing groups affect further substitution of benzene?

A

Makes the ring less susceptible to electrophilic substitution as the electron density of the ring decreases.

25
Q

What are examples of electron withdrawing groups?

A

NO2, COCL

26
Q

To which positions will further substitutions go if an electron withdrawing group is attached to the benzene ring?

A

3, 5