Chapter 8

Question 1

Délocaliser and localized electrons

Answer 1

Delocalized are shared by three or more atoms

Localized belong to a single atom or are shared by two

Molecule must be planar

When both resonance structures are equally stable, it’s the best option

Hybrid will look like most stable resonance contributor

Question 2

Benzene

Answer 2

Delocalized électrons, no double or single bond, all 1 1/2 basically

Electrons in pi bonds are the ones that move

6 pi (6 electrons that belong to pi bond are Delocalized)

Question 3

Benzene

Answer 3

Delocalized électrons, no double or single bond, all 1 1/2 basically

Electrons in pi bonds are the ones that move

6 pi (6 electrons that belong to pi bond are Delocalized)

Question 4

Molecular orbital

Answer 4

Contruncted by atomic orbital

Question 5

Cyclooctatetraene

Answer 5

Reacts like alkene
No p orbital overlap because not planar
Cannot be planar due to angle strain

Question 6

Resonance energy

Answer 6

Energy of contributor is much higher than energy of hybrid of resonnnance (actual structure)

Difference is called resonance energy or délocalisation energy

delocalization energy is the extra stability a compound has as a result of having delocalized electrons.

Question 7

Stability of resonance contributor

Answer 7

Complète octets are better

Negative charge on most electronegative atom

Positive charge on the l’est electronegative atom

No sperated chatges (no positive and negative if it can be neutral)

Question 8

Isolated and conjugated diene

Answer 8

Isolated: 2 single bonds separating the double bonds, reacts as 2 separate alkenes,

Conjugated: 1 single bond separating double bonds, electrons more Delocalized, treated resonance energy

Question 9

Heat of hydrogenation

Answer 9

The smaller the heat of hydrogenation is, the more stable the compound is

Difference in heat of energy between molecule with resonance and one without is the resonance energy and how much more stable it is

Question 10

Cumulated diene/cumulenes

Answer 10

2 double bonds right next to each other

Creates non superimposable enantiomers, even if they don’t have a chiral center

Question 11

Stability conjugated isolated cumulated

Answer 11

Conjugated>isolated>cumulated

Conjugated has more delocalization energy than isolated, so more stable
Also bond between the two sp2 carbons is stronger because shorter bonds

Question 12

Benzyl group and phenyl group

Answer 12

Benzyl: benzene and methyl group
Phenyl: just bezyl group

Benzylic carbon: not part of the benzene

Question 13

Allylic cation

Answer 13

Allyl with cation, very stable because lots of resonance energy because all resonance structures are equivalently stableo

Question 14

Ortho para

Answer 14

Ortho: on side of substituent

Para: opposite to it

Question 15

Order of stability

Answer 15

Benzene, allyl, and tertiary carbocation

Benze and allyl have resonance, making them more stable

Question 16

Resonance and acidity

Answer 16

More resonance, lower pka, more acidic

Resonance of conjugate base is the important one, so conjugate base is more stable so reaction occurs more

Question 17

Electronic effects

Answer 17

Electron donation decrease acidity because the conjugate base is less stable

Opposite for electron withdrawal

Electron donation can be done by anything with a lone pair

Electron withdrawing group don’t have a lone pair, and all have a carbon or nitrogen or sulfur with a double bond to oxygen, (or sometimes triple to nitrogen)

Alkyl groups are slightly electron donating by induction
OR are electron donating by resonance

Halogens are electron withdrawing by induction

Question 18

Aromatic

Answer 18

Benzene very stable because aromatic

Called aromatic, means extra stability than expected, caused bye uninterrupted cloud of pi electrons

Odd number of pairs or pi electrons is what you need to be aromatic (odd number of double bonds + negative charges)

Must be cyclic, planar and every ring atom has a p orbital (sp2 carbon)

Question 19

How benzene reacts

Answer 19

Electrophilic aromatic Substitution reaction: Replaces one of its H with the electrophile it is reacting with