ROH & Phenol Flashcards
(31 cards)
How do u name alcohols ?
(C no.) - sub alkyl - (longest C chain) - (C no.) -ol
How does BP of ROH compare to R and why ?
BP of ROH is higher than R
There are intermolecular Hydrogen bonds between ROH molecules, which are stronger than idid interactions between R molecules.
Why does solubility of ROH decreases with increasing C chain length ?
Energy released from forming hydrogen bonds with H2O is insufficient to over increasingly stronger id-id interactions between alkyl chains
Why isn’t ROH acidic ?
ROH —> OH- + H+
the conjugate base (OH-) of the dissociation of ROH is very unstable due to electron-donating inductive effect of alkyl group which intensifies the negative charge on OH-
Since CB is unstable, POE lies to the left
How can ROH be obtained
- E addition to Alkenes
- Nu sub of RX
- Reduction of carboxylic acids (primary ROH)
- Reduction of aldehydes (primary ROH)
- Reduction of ketones (secondary ROH)
What are the reactions that ROH can undergo ?
- Complete combustion
- Nu sub to RX
- Acid-metal redox
- Oxidation to COOH / COH / CO
- Dehydration to Alkenes
- Condensation to esters
- Idoform
Describe complete combustion
Nu sub of ROH, what are the possible reagents used and what do they form ?
- PX3 with heat
— RX + H3PO3 - PCl5 at rtp
— RX + PCl3 + HCl (g) - SOCl2 with heat
— RX + SO2 + HCl (g) - dry HX (g) with heat
— RX + H2O
What is the distinguishing test for -OH groups in ROH and CA
- Add PCl5 at rtp / SOCl2 with heat
+ve Observations:
White fumes evolved (HCl gas)
2.
Why is heat needed for Nu sub using PX3 but not for PCl5 ?
PCl5 is less sable than PX3
PX3 is more stable because there is less repulsion due to larger bond angle
Describe the acid-metal reaction
RO-Na+ forms
What is the distinguishing test for -OH groups in ROH, Phenol and CA ?
Add NA metal
+ve observations:
Effervescence, extinguish lighted splint with pop sound (H2 gas)
Do all ROH undergo oxidation ?
NO
Only primary and secondary
What is the products form when
1. Primary
2. Secondary
ROH undergo oxidation
- Aldehyde / CA
- Ketones
Describe oxidation of ROH to form aldehyde
Primary ROH
Add K2Cr2O7 in dilute H2SO4
Heat with immediate distillation
Describe oxidation of ROH to form CA
Primary ROH
Add K2Cr2O7 in dilute H2SO4
Heat under reflux
Describe oxidation of ROH to form ketone
Secondary ROH
Add K2Cr2O7 in dilute acid
Heat under reflux
What is the distinguishing test for primary secondary nd tertiary ROH ?
Add K2Cr2O7 in dilute H2SO4 and heat
Observations:
- orange to green: primary / secondary ROH
- remain orange: tertiary ROH
Dehydration to Alkenes
1. r&c
2. Mechanism
- Excess conc H2SO4 with heat
- — alkene + H2O
What rule applies to dehydration of ROH to Alkenes ?
Saytzeff rule: forms more substituted alkene
(More alkyl group attached to C=C)
Condensation to esters
Alcohol + carboxylic acid
What is the distinguishing test for ROH with H-C(CH3)-OH group ?
Add I2, NaOH (aq) with heat
+ve observations:
Yellow PPT (CHI3)
Why is Phenol more acidic than ROH ?
—OH —> —O- + H+
The conjugate base (—O-) form by the dissociation of phenol is stable due to the delocalisation of the lone pair of electrons on —O- into the benzene ring, disperse nagtive charge on —O- hence it is stable.
How does
1. Electron donating groups
2. Electron withdrawing groups
affect acidicty of phenol ?
- E.g: alkyl
Electron donating hence increase electron density on —O-, intensify negative charge, destabilising the CB
Hence acidity decreases - E.g: ENE groups
Electron withdrawing hence decrease electron density on —O-, dispersing negative charge, stabilise the CB Hence
Hence acidity increases
