W19 The language of Organic Chem, Isomerism Flashcards
What makes carbon so special?
- 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
What does reactivity of a molecule derive from?
Its functional groups
What are hydrocarbons?
What are examples?
Compounds composed entirely of carbon and hydrogen
Alkanes, alkenes, alkyne, aromatic, alkyl halide (haloalkane)
What is Functional Group Interconversion (FGI) ?
Is the process that allow a synthetic chemist to transform a functional group into another to change molecular properties
Ester Vs Ether
Ester- OH and COOH, O Between C and Carbonyl group (COOC)
Ether- Two Carbon chains bonded with O in middle (COC)
What is meant by Tert- Buthyl?
3 methyl groups attached to a carbon atom
Systematic name of a compound:
What are the definitions of..?
Parent=
Prefix=
Infix=
Suffix=
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
IUPAC rules: (suffix group)
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
Systematic nomenclature IUPAC:
Steps in naming a compound (4)
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:
Configurational Isomers: (R) and (S) system:
What are the steps/priorities in assigning R or S to a compound?
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)
What is an aromatic compound?
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
Aromatic compounds meet the following criteria:
- Structure must be cyclic, containing some number of conjugated pi bonds
- Each atom in the ring must have an unhybridized p orbital. Usually sp2 or occasionally sp hybridised
- 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
- Delocalisation of the pi electrons over the ring must lower the electronic energy
What is an Antiaromatic compound?
Meets the first three criteria, but delocalisation of the pi electrons over the ring increases the electronic energy
What is a Nonaromatic compound (aliphatic)?
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
What is Hückel’s Rule?
If the number of pi-electrons in the cyclic
system is:
(4N + 2), the system is aromatic
(4N), the system is antiaromatic
Heterocyclic compounds
, with rings containing sp2 hybridised heteroatoms
Polynuclear aromatic hydrocarbons
Two or more fused benzene rings. Fused
rings share two carbon atoms and the bond between them
e.g. Naphthalene, Anthracene
Reactions unique to aromatic compounds
- Electrophilic aromatic substitution
- Nucleophilic aromatic substitution
- Organometallic Couplings
- Addition reactions
- Side-chain reactions
- Oxidation of phenols to quinones
Resonance stabilised carbocation
Positive charge and double bond can move around and essentially swap places
Electrophilic Aromatic Substitution
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
Electrophilic Aromatic Substitution (electrophiles)
a. Bromination of Benzene
b. Nitration of Benzene
c. Sulfonation of Benzene
d. The Friedel–Crafts Alkylation
e. The Friedel–Crafts Acylation
Friedel crafts
Benzene ring replaces halogen
Activating, Ortho, Para-Directing Substituents
Methyl group: electron-donating (ED): stabilises the sigma complex (as it contains a carbocation with + charge)
Deactivating, Meta-Directing Substituents
- Nitrobenzene: 100,000 times less reactive. Nitro: strong deactivating group
- 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
The Heck Reaction
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
The Suzuki Reaction (Suzuki Coupling)
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
Phenol to Ether
Deprotonate to create a strong nucleophile
Conversion of ketones to alcohols: R-MGX
Organometallic reaction using Grignard reagent
How are Ketones converted to alcohols?
By reduction
Using NaBH4-sodium tetraborohydride
(^only for aldehydes and ketones)
Lithium aluminium hydride vs Sodium borohydride (NaBH4)
Lithium aluminium hydride can be used to reduce ANY carbonyl compound whereas NaBH4 is only for aldehydes and ketones
