alcohol and derivatives Flashcards
describe the functional groups and their oxidations
none -> hydrocarbon -alkane (-4,0 ox. number)
C=C bonds -> alkene (-2,0)
C-C triple bonds -> alkyne (-1,0)
aromatic system -> hydrocarbon (-1,0)
hydroxyl -OH-> alcohol (-2,+2)
oxide -O- -> ether (-2,+2)
carbonyl C=O -> aldehyde/ketone (0,+2)
carboxylic acid -COOH -> organic acid (+2,+3)
ester -CO-OR -> ester (+2,+3)
amine C-N -> amine (-2,+1)
amide -CONH- -> amide (+2,+2)
REMINDER: oxidation state depends on the electronegativity difference with bonded atoms
-oxidation is breakdown processes, reduction is synthesis
- attached atom is more electronegative -> oxidation number is increased by 1 (F>O>N, Cl>Br>C>H)
- viceversa (with H) the oxidation is decreased by 1
nomenclature of alcohols
- alkane name is changed to include -ol suffix
- 3 or more C atoms -> specify the position of the substituent with lowest possible number
- cyclic alcohols with multiple substituents -> assign numbers, alcohol always on 1 (when there are substituents they get the 2nd lowest number after OH)
- benzene -> phenol
alcohol properties
- C-O bond is polarised due to large electronegativity difference (charge in not evenly distributed) giving partial positive charge on carbon atom
- causes reactivity
- -OH group can form intermolecular hydrogen bonds in pure substances and water
- acts both as donor and acceptor
- lone pairs on Oxygen makes the alcohol a nucleophile
- generally all liquids
- short chain= water soluble
- longer chain (>5) = insoluble
- long alkyl chain are more hydrophobic
- lower energy achieved when they cluster together
- disinfectants, paint thinners and recreational purposes
describe the properties of thiols
SH:
- poor hydrogen bond acceptor -> more volatile
- S-H bond is longer and weaker than O-H
- more acidic as dissociation of proton is easier
- present in several important biomolecules (Coenzyme A, lipoamide…)
- reacts with acids to form thioesters, forming a high energy bond
describe the properties of ethers
O atom bridging two alkyl or aromatic groups:
- form dipoles opposite O atom
- can accept H but can’t donate H (no OH group)
- makes them more volatile
- poorly soluble in water
- used as anaesthetics
what is the nomenclature of ethers?
the shorter chain is named alkoxy group, the longer chain the corresponding alkane
how are alcohols classified?
primary: 1 C attached to central C
secondary: 2 C attached to central C
tertiary: 3 C attached to central C
how do reactions different between alcohols?
- primary alcohols can be oxidised to aldehydes
- has 2 free H which can be removed
- secondary alcohols can be oxidised ketones
- has 1 free H which can be removed
- tertiary alcohol has no reaction as it has not free H around C
what is the reactions of phenols?
phenols can be oxidised to quinones (electron transport)
what is the reaction between alcohols and acids?
alcohol + acid (organic/inorganic) -> esters
- substitution -> -OH acts as nucleophile and the acid is catalysed
how is an alkene obtained from an alcohol?
elimination of water to allow the formation of a double C bond
- acid is catalysed -> H3O+ is used then obtained again through H donation
describe the mechanism of acid/base equilibria
R-OH + H2O R-O- + H3O+
- chain attached to negative O has electron-donating properties which stabilises the charge
- the longer the chain, the higher electron-donating property, the more stabilised the base
- phenols’ negative charge is stabilised by resonance in the ring, giving it a higher pKa (phenolate ion)
- double bond can then move in the ring -> resonance structures stabilise the charge
alkyl acid base mechanism
very weak acids (pKa - 16-18)
- groups that stabilise negative charge on teh conjugated base (electron withdrawing) make the alcohol more acidic (e- donors more basic)
phenols acid base mechanism
pKa -> 10
- negative charge in conjugate base is stabilised by resonance
thiols acid base mechanism
more acidic than corresponding alcohols
- sulfur can disperse charge over a larger volume (more polarizable)
- thiolates are good nucleophiles since lone pairs are less attracted by the atom (lower electronegativity
- thiols can be oxidised to acid forms
- cysteine (amino acids) ca be oxidised to variety of acid forms -> two cysteine react under oxidising conditions to form disulfide bond
