W19 The language of Organic Chem, Isomerism

Question 1

What makes carbon so special?

Answer 1

• Four valence electrons → tetravalent: carbon forms four bonds
• It forms strong, stable covalent bonds to itself, to hydrogen, and to other second-row elements
• It readily forms multiple bonds (sharing two or three electrons)
• It readily forms long chains

Question 2

What does reactivity of a molecule derive from?

Answer 2

Its functional groups

Question 3

What are hydrocarbons?
What are examples?

Answer 3

Compounds composed entirely of carbon and hydrogen
Alkanes, alkenes, alkyne, aromatic, alkyl halide (haloalkane)

Question 4

What is Functional Group Interconversion (FGI) ?

Answer 4

Is the process that allow a synthetic chemist to transform a functional group into another to change molecular properties

Question 5

Ester Vs Ether

Answer 5

Ester- OH and COOH, O Between C and Carbonyl group (COOC)

Ether- Two Carbon chains bonded with O in middle (COC)

Question 6

What is meant by Tert- Buthyl?

Answer 6

3 methyl groups attached to a carbon atom

Question 7

Systematic name of a compound:
What are the definitions of..?
Parent=
Prefix=
Infix=
Suffix=

Answer 7

Parent- Length (number C) of main chain
Prefix- Can be one or more, additional info e.g.
substituents, other functional groups, cyclic molecule
Infix= Unsaturation of main chain (single, double, triple C-C bond)
Suffix= Dominant functional group + its position if needed

Question 8

IUPAC rules: (suffix group)

Answer 8

Always give the lowest number possible to the SUFFIX group, e.g. between an alcohol and amine, you prioritise the alcohol and number it the lowest

Question 9

Systematic nomenclature IUPAC:
Steps in naming a compound (4)

Answer 9

1st Step: Identify the longest continuous carbon chain (i.e. longest unbroken chain of carbon atoms in a given molecule). This becomes the Parent.
2nd Step: Identify unsaturation (any double or triple bond?). Choose the Infix (an, en or yn)
3rd Step: number each carbon atom in the principal chain so that the group attached to the chain (the substituent) has the smallest possible number
4th Step: name the substituent. This becomes the Prefix to the principal chain and number. Decide the Suffix. Here it is easy, one C is attached to the principal chain:

Question 10

Configurational Isomers: (R) and (S) system:
What are the steps/priorities in assigning R or S to a compound?

Answer 10

1) Priority: from 1 to 4. Assigned on the basis of atomic number.
Higher atomic number gets higher priority
2) Substituents: if no priority, the next set of atoms in the unassigned groups is examined
3) Double or triple bonds: assigned priorities as if both atoms were duplicated or triplicated
4) Arrange (rotate) the molecule: group 4 is pointing away from the viewer

If the lowest-priority atom (usually H) is oriented toward you, you don’t need to turn the structure around. You can leave it as it is, find the (R) or (S) configuration, and reverse the answer.

S= Anticlockwise
R= Clockwise (right)

Question 11

What is an aromatic compound?

Answer 11

A cyclic compound containing some number of
conjugated double bonds and having an unusually large resonance energy
e.g. Benzene

C-C bonds in benzene are all equal - 1.4Å (single C-C 1.54Å, double C=C 1.33Å)

Resonance hybrid of the two Kekulé structures: the pi electrons are delocalised

Question 12

Aromatic compounds meet the following criteria:

Answer 12

1. Structure must be cyclic, containing some number of conjugated pi bonds
2. Each atom in the ring must have an unhybridized p orbital. Usually sp2 or occasionally sp hybridised
3. Unhybridized p orbitals must overlap to form a continuous ring of parallel orbitals (conjugated). Structure must be planar (or nearly planar) for effective overlap to occur
4. Delocalisation of the pi electrons over the ring must lower the electronic energy

Question 13

What is an Antiaromatic compound?

Answer 13

Meets the first three criteria, but delocalisation of the pi electrons over the ring increases the electronic energy

Question 14

What is a Nonaromatic compound (aliphatic)?

Answer 14

Cyclic compound that does not have a
continuous, overlapping ring of p orbitals. Its electronic energy is similar to that of its open-chain counterpart

Question 15

What is Hückel’s Rule?

Answer 15

If the number of pi-electrons in the cyclic
system is:
(4N + 2), the system is aromatic
(4N), the system is antiaromatic

Question 16

Heterocyclic compounds

Answer 16

, with rings containing sp2 hybridised heteroatoms

Question 17

Polynuclear aromatic hydrocarbons

Answer 17

Two or more fused benzene rings. Fused
rings share two carbon atoms and the bond between them
e.g. Naphthalene, Anthracene

Question 18

Reactions unique to aromatic compounds

Answer 18

1. Electrophilic aromatic substitution
2. Nucleophilic aromatic substitution
3. Organometallic Couplings
4. Addition reactions
5. Side-chain reactions
6. Oxidation of phenols to quinones

Question 19

Resonance stabilised carbocation

Answer 19

Positive charge and double bond can move around and essentially swap places

Question 20

Electrophilic Aromatic Substitution

Answer 20

Step 1: Attack on the electrophile forms the sigma complex (a resonance-stabilised carbocation)
Step 2: Loss of a proton regains aromaticity and gives the substitution product

Overall reaction: substitution of an electrophile (E+) for a proton (H+) on the aromatic ring

Question 21

Electrophilic Aromatic Substitution (electrophiles)

Answer 21

a. Bromination of Benzene
b. Nitration of Benzene
c. Sulfonation of Benzene
d. The Friedel–Crafts Alkylation
e. The Friedel–Crafts Acylation

Question 22

Friedel crafts

Answer 22

Benzene ring replaces halogen

Question 23

Activating, Ortho, Para-Directing Substituents

Answer 23

Methyl group: electron-donating (ED): stabilises the sigma complex (as it contains a carbocation with + charge)

Question 24

Deactivating, Meta-Directing Substituents

Answer 24

1. Nitrobenzene: 100,000 times less reactive. Nitro: strong deactivating group
2. One product: meta-directors, deactivate the meta position less than the ortho/para positions, allowing meta substitution

Inductively withdraws electron density from the aromatic ring, which is less
electron-rich, so deactivated

Question 25

The Heck Reaction

Answer 25

Coupling of an aryl or vinyl halide with an alkene to give a new C-C bond at the less substituted end of the alkene, usually with trans stereochemistry.

alkane reacts with alkyl halide

Question 26

The Suzuki Reaction (Suzuki Coupling)

Answer 26

Palladium-catalysed substitution that couples an aryl or vinyl halide with an
alkyl, alkenyl, or aryl boronic acid or boronate ester

An aryl halide with an arylboronic acid, using palladium on carbon and water
asthe solvent

Question 27

Phenol to Ether

Answer 27

Deprotonate to create a strong nucleophile

Question 28

Conversion of ketones to alcohols: R-MGX

Answer 28

Organometallic reaction using Grignard reagent

Question 29

How are Ketones converted to alcohols?

Answer 29

By reduction
Using NaBH4-sodium tetraborohydride
(^only for aldehydes and ketones)

Question 30

Lithium aluminium hydride vs Sodium borohydride (NaBH4)

Answer 30

Lithium aluminium hydride can be used to reduce ANY carbonyl compound whereas NaBH4 is only for aldehydes and ketones