organic chemistry 3

2 example of benzene derived, aromatic compounds

phenol: benzene-OH

* acts as an acid

aniline: benzene-NH2

* acts as a base



both more reactive than benzene

phenol

= acts similar to alcohol i.e. H bonding
= more acidic than alchohols
= deprotonated in basic conditions to from phenoxide
-ve charge on OH or O group can be delocalised to within ring for stability

aniline

= less basic than alkyl amines
= protonated in acidic conditions to form anilinium cation
-ve charge on ring in aninline ONLY can be delocalised to within ring for stability

relatice reactivites of aromatic compounds

aniline > phenoxide > phenol > benzene > anilium cation

carbonyl compounds

compounds with C=O group
- aldehydes & ketones
- carboxylic acids, esters, anhydrides, acid halide, amide
= all with sp2 hybridised C, planar

carbonyl nucleophilic addition

e pair of Nu attack sp2 planar C. sp3 tetrehedral C intermediate formed. e pair from O- pushed onto LG. sp2 planar C formed.
LG = must be stable sink for e density

relative reactivity of carbonyl nucleophilic addition

aldehyde > ketone ( more e at C )
ester ≈ carboxylic acid > amide

carbonyl nucleophilic addition leaving groups

alkoxy > hydroxy > alkyl > H

carbonyl nucleophilic addition mechanism with no good LG

i.e. three alkyl groups
acid workup (H+ from H3O+) to produce alcohol and water

spectroscopy

interaction of matter with light to probe the chemical structure

* compound absorbed certain wavelengths of white light and gives out different colour light

how does wavelength relate to energy?

low wavelength = high energy
high wavelength = low energy

Infrared spectroscopy

= used to identify functional groups
= finds v for frequency of bond stretching vibration

infrared spectroscopy graphs

= functional groups can be identified by peaks in earlier region by their constituent bonds
= compounds with similar functional groups identified by the 'fingerprint region' (most unique)
i.e. carboxylic acid hard to distiguish carbonyl alcohol

amines

= basic, therefore water soluble
= nucleophilic
= some basic but non-nucleophilic because of hindered lone pair
= weak H bond acceptors and donors (weak NH dipole)
= therefore, lower b.p. than alcohols

amine preparation

-alkylation of ammonium for primary amine
= R-X + NH3 → R-NH2 + X-NH4
-reduction of R-NO2 for primary amine
= R-NO2 + H2 (Ni catalyst) → R-NH2
-reduction of nitryl groups for primary, secondary and teriary
= R≡N + base → R-NH2(H2) (protonated)
= R(=O)-NR' → R(H2)-NR'

relative reactivity of ketones and aldehydes

aldehydes > ketones
= both dipolar (posess dipole) and aprotic (no dissocietable protons)
= aldehyde carbocation less hindered
= ketone has more e- donating groups on carbonyl C, so less partially +ve

ketone and aldehyde nucleophilic addition

only preferred leaving group is the nucleophile being added. when a strong nucleophile is used, the bond is too strong to act as the leaving group. the oxygen anion can be protonated to form alcohol

alcohol formed
aldehydes = secondary
ketones = tertiary

ketone and aldehyde hydride addition

(hydride = hydrogen anion)
hydride acts as nucleophile. again, no good LG so after acid workup, alcohol is formed.

alcohol formed
aldehydes = primary
ketones = secondary

ketone and aldehyde reduction

aldehydes = primary alcohols
ketones = secondary alcohols

ketone and aldehyde oxidation

aldehyde = carboxylic acid
ketone = NO REACTION

imine and formation

= aromic groups increase stability by π bonds

amine + aldehyde/ketone (acid and base catalysed) → imine

oxime

2 types

* ketoxime with two R groups: ketone + hydroxyamine
* aldoxime with one R group and one H group: aldehyde + hydroxyamine

acetal and formation

= unreactive (too bulky)
ketone + 2 x alchohol

carboxylic acid

= acidic
= intermolecular hydrogen bonding
= delocalised e- between two O's
= salts of cation form soap and salts of divalent cation form soap scum

carboxylic acid synthesis

- primary alcohol oxidised to carboxylic acid
- benzene oxidised to benzoic acid
- CO2 reacted with grignard reagent forms carboxylic acid salt
- cyanide hydrolised to carboxylic acid

pKa

= -ve log of the dissociation constant (Ka)
= describes position of equilibrium
= inversely describes stability of anion ( > anion stability = < pKa i.e. enegativity of R' group > )

dissociation constant (Ka)

pH equation

used to find ratio of molecule to ions i.e. acidity
( < number of ions = < acidity)

acyl derivates

= formed from carboxylic acids
-acid chloride
-acid anhydride
-thioester
-ester
-amide

relative reactivites of acyl derivatives

acid chloride > acid anhydrides > thioester >> ester > amide
= < pKa of conjugate acid, > reactivity

acid chloride and reactions

= good electrophiles & react with weak nucleophiles since strong carbocation
= hydrolysed to form carboxylic acid and HCl
R-C(=O)Cl + H2O > R-C(=O)OH + HCl
= nucleophilic attack under basic conditions form ester
= ammonia acts as base and nucleophile to form primary amide

acid anhydrides
-formation
-reactions

= moderate electrophiles

= acid + acid chloride > acid anhydride + chloride ion
= carboxylic acids + heat > acid anhydride + H2O

= acid anhydride + primary amine > amide + LG + hydrised base

choosing leaving groups

= choose the LG with the lowest pKa of conjugate acid, since the stability of the anion will be highest

esters

= H bond acceptors (∂- O)
≠ H bond donors (no ∂+ H)
= low b.p. since no full H bonding

ester synthesis

Fishcer esterification
= alcohol acts as nucleophile and attack carboxylic acid. base deprotonates and smallest OH group acts as LG.

= non nucleophilic base (too bulky) deprotonates OH of carboxylic acid and O lp attacks R of alkyl halide. ester and salt formed of base and halide anion. e

ester reactions

base hydrolysis
= forms carboxylic acid and O(-)-R'. charge passed to form oxide (more stable)
reduction to alcohol
= 2 x nucleophilic attack with hydride forms primary alchohol
= 2 x nucleophilic attack with grignard reagent forms tertiary alchohol
transferification with strong base
= deprotonated alc acts an Nu and swtiches with O-R group

activated esters

highly susceptible to nucleophilic attack

thioesters and formation

carboxylic acid and thoil derivatives
> electrophilic than esters
= S-R group can be exchanged by HS-R', catalysed by base

= HS-R acts as nucleophile and base deprotonates

amide and formation

= planar = partial double bond between O, C & N
≠ basic
≠ nucleophilic
= strong H bonds since both accept (∂- O) and donate (∂+ H)
secondary amides:
cis bonds
= R & R' on same side
trans bonds
= R & R' on opposite sides

= nucleophilic addition of amine to carboxylic acid derivative

amide reactions

carboxylic acid + amine ⇌ amide
( > dehydrolyse, < hydrolyse) (H2O)