Alcohols, phenols and ethers Flashcards
Alcohol Outline
Hydroxyl (OH) group bound to a tetrahedral C. 4 C to C single bonds with 109.5 degrees between them
Primary alcohol Outline
C attached to hydroxyl group is attached to 1 substituent other then H
Secondary Alcohol Outline
C attached to hydroxyl group is attached to 2 substituents other then H
Tertiary Alcohol Outline
C attached to hydroxyl group is attached to 3 substituents that aren’t H
Properties of alcohols
C (delta positive) is less electronegative then O (delta negative). Have higher boiling points then alkanes (due to H bonding). Soluble in water if C chain <5. Have a hydrophobic (C Chain) and hydrophilic (OH) region. Weak acids (dissociate slightly in water donating H to water)
Relationship between conjugate base stability and acidity
More stable conjugate base = equilibrium favouring base = increased acid dissociation = stronger acid
Measure of stability of conjugate base
The slower it is to accept it’s proton back from the water = the more stable the base
Properties of an alcohol’s conjugate base
A negatively charged O (due to a loss of H). Charge can be spread/localised
Electron withdrawing substituents effect
Pull electrons away from charged atom and thus spread charge over multiple atoms of the same molecule. This stabilises molecule (conjugate base) = increases acidity of alcohol. Eg; halogens
Electron Donating Substituents Effect
Push electrons onto charged molecule thus more intensely localising charge. This decreasesv stability of molecule (conjugate base) = decreasing the acidity of alcohol. Egs; alkyl groups
Which type of alcohol is the most acidic
Primary, least amount of alkyl groups.
Which type of alcohol is the most alkaline
Tertiary, most amount of alkyl groups.
Reaction preparation of alcohols
Esters hydrolysed to carboxylic acids and alcohols
Reactions with alcohols
Dehydration (loss of H2O) and Oxidation (loss of H)
3 steps of dehydration of an alcohol
Alcohol catalysed by acidic catalyst, loss of water, loss of proton
Protonation of alcohols
OH when neutral is a poor leaving group. It is ionised by an acidic catalyst to make it a good leaving group (H bonds to OH leaving O positively charged)
Loss of water outline
Positive O attracts both electrons in it’s bond with C. This breaks the bond releasing H2O from molecule and leaving a positively charged carbocation (forms most stable intermediate possible)
Which is the most stable carbocation
Tertiary
Which alcohol is most reactive in dehydration
Tertiary (least reactive = primarary)
Loss of a proton Outline
The positively charged C attracts electrons from a bond the neutral C has with a H. These 2 electrons form a pi bond (second bond) between 2 Cs, neutralising C. H is unattached from molecule reforming catalyst
Zaitzev’s Rule Outline
The alkene with more substituents other then H will be formed preferentially
Primary Alcohol Oxidation Path
Alcohol to Aldehyde (loses 2 Hs) to Carboxylic Acid (gains O)
Secondary Alcohol Oxidation Path
Alcohol to Ketone (loses 2 Hs)
Tertiary Alcohol Oxidation Path
N/A
Enzyme that converts alcohol to an aldehyde
alcohol dehydrogenase (can also be done biologically by NAD+)
Enzyme that converts an aldehyde to carboxylic acid
aldehyde dehydrogenase
Breathalyser Mechanism of action
Potassium dichromate is an oxidising agent for ethanol. Reducing itself to Chromium 3 sulfate
Application of ethanol
Antiseptic (bactericidal/bacteriostatic) on skin. Disinfectant on non-living tissues. Most effective at 60-70%
Phenol Outline
Triagonal planar, attached C with OH attached to 3C atoms
Phenol Acidity
Stronger then alcohols (conjugate bases are more stable as they’re stabalised by resonance, alkoxides aren’t).
Ethers Outline
Oxygen bonded to 2 organic groups (alkyl and aryl). No H bonding (lower boiling points then alcohol).
Mesomeric Effects Outline
Inductive and resonance effects
Inductive Effects Outline
Oxygen being more electronegative then C pulls electrons
Resonance Effects Outline
Lone electrons interact with pi electrons. Stronger then inductive
Conjugation of Double Bonds
Higher density of electrons. Electrons shared between alternating double and single bonds increase stability
