Organic reactions

What 3 basic reactions exist in organic chem?

Addition, Substitution and Elimination

Link the 3 basic organic reaction types to saturation

Addition: Increases saturation at the carbon

Substitution: degree of saturation remains unchanged

Elimination: Decreases saturation at the carbon

What are 3 classification descriptors for organic reagents and substrates based on their electron ?

reagents and substrates with an unpaired electrons are called radicals while reagents and substrates with paired electrons are either electrophiles or nucleophiles

Nucleophile

any atom, molecule or ion that donates a pair of electrons to an electrophile to form a new covalent bond

(they are electron rich)

Characteristics of a nucleophile

Nucleophiles have one or more of these properties:

- They have a negative charge (full negative charge or slightly negative charge)

- They have a lone pair

- They have a pi bond

Electrophile

any atom, molecule or ion that accepts a pair of electrons from a nucleophile to form a new covalent bond

(they are electron poor)

Characteristics of an electrophile

Have one or more of the following:

Positive charge (Slightly positive or fully positive)

Vacant orbitals to accomodate donated electrons

Have a site with positive polarity

radicals

have a single unpaired electron and are very reactive

What reactions do alkanes undergo

elimination, substitution or combustion

Why are alkanes the least reactive organic compounds?

- Strong c-c bond

- lack of polarity

- no lone pairs or vacant orbitals

- no major sites of reactivity

What reagents are used in organic reactions involving alkanes

Free radicals

Explain the radical substitution an alkane undergoes using the chlorination of an alkane in which the overall reaction is. (Reaction condition: light or heat)

CH4 + Cl2 --> CH3Cl + HCl

What reactions can alkenes and akynes undergo?

Electrophilic addition

4 types of electrophilic addition reactions alkenes and alkynes undergo?

1) Hydrogenation (addition of H2):

2) Halogenation (addition of X2)
3) Hydrohalogenation (addition of HX)
4) Hydration (addition of H2O)

What products are made from hydrogenation of an alkene or alkyne? Mention any reaction conditions if needed

They both produce an alkane

Reaction condition: Pt or Pd catalyst

What products are made from halogenation of an alkene or alkyne? Mention any reaction conditions if needed

A haloalkane (alkyl halide): Specifically one that is disubstituted

* meaning it will be an alkane with two chlorine or bromine atoms attached.

What products are made from hydrohalogenation of an alkene or alkyne? Mention any reaction conditions if needed

A haloalkane with one halogen attached. It will either make a symmetrical or asymmetrical alkyl halide in which a major and minor product will be formed.

(NB)

Draw the reaction mechanism of the hydrohalogenation of an asymmetrical alkene (eg propene)
in order to name the major and minor product

What is markonikov’s rule

In the addition of HX to an alkene, the H becomes attached to the carbon with fewer alkyl substituets. Conversely, the X group always bonds to the carbon with more alkyl substituents (R-group)

Stability order of carbocations (most stable to least)

1) Tertiary carbocations

2) Secondary carbocations

3) Primary carbocation
4 ) Methyl carbocation

What products are made from hydration of an alkene or alkyne? Mention any reaction conditions if needed

An alcohol as well as reformed acidic catalyst (eg H+)

Reaction conditions: H+ catalyst and heat

Why is an acid catalyst needed?

The H-O-H bonds make for a poor electrophile as there is no leaving group. Therefore a strong H+ bond is needed to protonate the double bond.

Write the reaction mechanism of the hydration of an alkene

Polarity of organometallic

The carbon is slightly negative and the metal will be slightly positive

What reactions do alkyl halides undergo?

nucleophilic substitution or elimination

Compare the nucleophilic substitution of a alkyl halide with the nucleophilic elimination of an alkyl halide

Substitution: The nucleophile attacks the carbon and produces (Alkyl group-Nu + X-) - usually alcohols

elimination: the nucleophile attacks a hydrogen bonded to carbon 2 (where carbon 1 is the substituted carbon). It produces an alkene + NuH + X-

both react with bases like NaOH

Write the reaction mechanism of nucleophilic substitution of an alkyl halide

Write the reaction mechanism of nucleophilic elimination of an alkyl halide

What favours elimination over substitution?

• Steric hinderance favours elimination

• High temperatures also favour elimination

Factors affecting the ease of reaction

1) The leaving group (how good of a leaving group is)

2) The strength of a nucleophile (better nucleophile means easier reaction)

Rank some common leaving groups and state whether they require an acid catalyst or not

1) R-Hal (good leaving group - not F^-)

2) R-OH & R-OR requires a catalyst to force the OH or OR group to leave.
3) R-NR2 (very poor leaving group)

polymer

large molecules made up of many identical repeating units/monomers

polymerisation

joining of monomers with low molecular mass to generate substances with high molecular mass

What do the physical properties of a polymer depend on

• The size of the macromolecule

• Increasing chain length: increase density, hardness, melting point

basic types of polymers depending on their formation

radical addition polymers, condensation polymers

Draw the reaction mechanism of radical addition polymer

What reaction conditions favour rapid polymerisation and what conditions favour large yield polymerisation

Rapid polymerisation:
- High temp

• High monomer concentration

• Catalysis

Large yield polymerisation:
- Low temp

• High monomer concentration

Condensation polymers

Polymers that form from monomers by the expulsion of a small molecule eg H2O.
The monomers involved contain two functional groups.

Examples of condensation polymer monomers

• amino acids: carboxylic acid + amine

• Diamines

• dicarboxylic acids

examples of condensation polymers

polyesters

polyamides

biopolymers

polyamides

formed when monomers are linked by an amide bond

what reactions do condensation polymers undergo

substitution

polyesters

formed when monomers are linked by an ester bond

Homopolymer vs copolymer

homopolymers are polymers that are made of one type of monomer while copolymers are made up on two or more different kinds of monomers

what reactions does benzene undergo

electrophilic substitution where x must be a good electrophile (unusual cations like Cl+, NO2+, CH3+

what specific electrophilic substitution reactions does benzene undergo?

• Halogenation (Cl2 or Br2)

• Alkylation (substitution with R group)

• Acylation (substitution with R-C=O)

products and conditions from the halogenation of benzene

• haloarene + HX + recovered catalyst

• condition: AlCl3, FeCl3, FeBr3

Reaction mechanism of the halogenation of benzene (Use Cl2)

products and conditions from the alkylation of benzene

Benzene + Haloalkane —> benzene with methyl substituent + HX + regenerated catalyst
Conditions: AlCl3 catalyst

products and conditions from the acylation of benzene

Benzene + Haloacyl —> benzene with acyl group substituent + HX + regenerated catalyst
Conditions: AlCl3 catalyst

What reactions do alcohols undergo?

• Elimination: Dehydration - Loss of H2O

• Dehydrogenation/oxidation: loss of H2

Order of reactivity of acid catalysed dehydration

1) Tertiary alcohols

2) Secondary alcohols

3) Primary alcohols

zaitsev’s rule

The alkene with more alkyl substituents on the double bond carbons will be the major product

what products and conditions are required for acid catalysed dehydration?

Each require a strong acid such as H2SO4.

Primary alcohols form 1 alkene + water + catalyst regenerated

Secondary and tertiary alcohols produce 2 possible products of alkenes + water + catalyst

Common oxidising agents

KMnO4, K2Cr2O7, CRO3, H2CrO4, PCC

When each of the alcohols (primary, secondary and teritiary) are dehydrogenation/oxidised what forms?

Primary alcohols will form a carboxylic acid. (UNLESS it is oxidised by PCC specifically; in that case it will form an aldehyde)

Secondary alcohols will form a ketone.

Tertiary alcohols DO NOT OXIDISE!

What reactions do ketones and aldehydes undergo?

Nucleophilic addition

Why are ketones and aldehydes super reactive

• polar bonds

• lone pairs on heteroatoms

• exposed pi electrons

Recall which additions we’re studying for the nucleophilic addition of aldehydes and ketones

amine, hydrogen cyanide, water, h2

What does the nucleophilic addition of NH3 and a primary amine produce when added to an aldehyde/ketone

an imine is produced (C=N-R)

What does the nucleophilic addition of HCN produce when added to an aldehyde/ketone

Aldehyde: A carbon with the following substituents:
- One R group
- OH

• CN (nitrile)

• Hydrogen

Ketone: A carbon with the following substituents:
- two R group
- OH

• CN (nitrile)

What products form as a result of the nucleophilic addition of water to a ketone/aldehyde?

• Geminal diol/hydrate = a compound where two -OH groups are bonded to one carbon

THIS requires an acid catalyst

What products form as a result of the nucleophilic addition of H2 to a ketone/aldehyde? (substrates are reduced)

What rxn conditions are used too?

An alcohol

NaBH4 LiAlH4 and H+

Composite functional groups

• Carboxylic acids

• Esters

• Acid halide

• Amides

what reactions do Composite functional groups undergo

• OVERALL: substitution

this substitution happens in two steps (addition then elimination)

Addition first occurs when the double bond of C=O breaks and the nucleophile bonds to the carbon. Elimination the happens in which the leaving group gets kicked out and reforms the double bond between C=O.

Leaving group examples:
- Carboxylic acids → OH- or H2O

• Esters → OR or OH

• Acid halides → X- (halide ion)

• Amides → NH2 (amine)

label top to bottom

1) carboxylic acid + HCl

2) Ester + HCl

3) Amide

4) Amide

label top to bottom

1) Carboxyllic acid
2) ?

3) Amide

label top to bottom

Ester

Amide
3)?