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La Chimie H2 > Alcools et Phénols > Flashcards

Alcools et Phénols Flashcards

1
Q

Give general formula and functional groups of alcohols

A

formula: CnH2n+1OH or ROH

*MUST CLASSIFY
func grp: primary/secondary/tertiary alcohol

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2
Q

Describe nomenclature of alcohols

A
  • For one alcohol, replace ‘e’ with -ol (and relevant number)
  • For two alcohol grp, leave ‘e’ with -ol (and number)
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3
Q

What are germinal diols

A
  • Compounds w 2 -OH grp bonded to same C atom
  • unstable, readily eliminate H2O molecule to form aldehyde or ketone

Extra case: if got three OH attached to 1 C, carboxylic acid is formed

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4
Q

What bonds form btw alcohol molecules? Why?

A

id-id and hydrogen bonds

bcos alcohol hv non-polar alkyl grp & polar -OH grp

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5
Q

Compare and explain differences in boiling points of alcohols and other similar Mr organic compounds

A

Alcohols hv much higher bp than hydrocarbon & other organic compounds of comparable size e- cloud due ti stronger intermolecular H bonding needing more energy to overcome

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6
Q

Why cannot use hydrogen bonding to explain difference in boiling point between alcohols with same no of -OH?

A

Bcos similar extent of intermolecular hydrogen bonding by alcohols

So, must use other factors eg
- surface area of contact (similar Mr: chain > branched)
- e- cloud size (diff Mr)

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7
Q

Explain solubility of alcohols

A
  1. completely miscible w water
    bcos
    - energy released by form n H bond btw alcohol & H2O enough to overcome H bond btw water molecules & H bond btw alcohol molecules
  2. solubility in water decrease as no of C atom in alcohol increase
    bcos
    - larger non polar R grp make alcohol more hydrophobic. Main interact n btw large alcohol molecules & H2O become id-id
    - energy released fr id-id attract n btw alcohol & H2O molecules inadequate to overcome H bond btw H2O molecules & H bond + id-id btw alcohol molecules
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8
Q

Strength of acid depends on…, which depends on …

A

stability of conjugate base (the more stable, stronger acid),

intensity of -ve charge (the more intense, the less stable)

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9
Q

Why are alcohols generally very weak acids, even less acidic than water?

A

e- donating alkyl (R) grp intensify -ve charge on conj base (alkoxide ion, RO-), thus destabilising conj base
=> lose proton less readily and acid strength decreases
ROH ⇌ RO- + H+

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10
Q

The higher the Ka, the … the acid

The lower the pKa, the … the acid

A

stronger

stronger (pKa=-lgKa)

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11
Q

What reactions do alcohols undergo?

A
  • Acid-metal displacement
  • Condensation/ nuc acyl sub n
  • Nuc Sub n
  • Elimination
  • Oxidat n
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12
Q

Name reagent, condit n & type of rxn of ROH + sodium

A

R&C: Na (or other reactive metal eg K)
Type of rxn: acid-metal displacemt

NOTE:
- Mole ratio is ROH = 0.5 H2
- alcohol no react w base bcos much weaker acid than water

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13
Q

Name reagent, condit n & type of rxn of ROH and carboxylic acids

A

R&C: RCOOH (specify specific acid if specific ester is stated), conc H2SO4 as cata, heat
type of rxn: condensat n/ nuc acyl sub n

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14
Q

Which part of an ester comes from acid and alcohol?

A

RC=O comes from acid,

OR’ comes fr alcohol

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15
Q

Name reagent, condit n & type of rxn of ROH + acyl chloride

A

R&C: RCOCl (specify acyl chloride if specific ester is stated)
Type of rxn: condensat n/ nuc acyl sub n

*Advantage: no heating needed, good yield of ester since rxn is irreversible

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16
Q

Name reagent, condit n & type of rxn of ROH to form RX

A

type: Nu Sub n

R&C:
- HCl (g), heat –> R-Cl + H2O
- anhydrous PCl5 –> R-Cl + POCl3 + HCl
- anhydrous PCl3 –> R-Cl + H3PO4
- anhydrous SOCl2 –> R-Cl + SO2 (g) + HCl (g)
- NaBr, conc H2SO4, heat/HBr (g), heat –> R-Br + H2O
- anhydrous PBr3 –> R-Br + H3PO4
- red P + I2 (PI3 is unstable) –> R-I + H3PO3

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17
Q

Why should water be absent (anhydrous) in reaction of alcohol with PX3, PCl5 and SOCl2?

A
  • PX3, PCl5 and SOCl2 undergo complete hydrolysis w water to give other side products, so yield of RX pdt decreases
18
Q

Why is SOCl2 preferred over PCl5 (or PCl3 or HCl)?

A

using SOCl2 means side pdt (SO2 & HCl) are gases, easier to separate fr rxn mix to obtain pure pdt R-Cl

19
Q

What is Saytzeff’s rule?

A

(for elimination rxn)
major pdt is alkene w more no R grp (more substituted alkene) attached to the C=C

20
Q

Name reagent, conditions, product obtained, observat n & general eqn of oxidation of primary alcohol (HINT: two types of oxidation)

A

Mild oxidation:
R: K2Cr2O7 (aq), H2SO4 (aq)
C: Heat w immediate distillat n
Pdt: aldehyde (RCHO)
Observ n: orange sol n turn green
eqn: RCH2OH + [O] –> RCHO + H2O

Strong oxidation
R: K2Cr2O7(aq) / KMnO4(aq), H2SO4 (aq)
C: Heat
Pdt: carboxylic acid (RCOOH)
Observ n: orange K2Cr2O7 sol n turn green/ purple KMnO4 sol n decolourise
Eqn: RCH2OH + 2[O] –> RCOOH + H2O

21
Q

Name reagent, conditions, type of reaction and general equation of oxidation of secondary alcohols

A

R&C: KMnO4(aq)/K2Cr2O7(aq), H2SO4(aq), heat
type: oxidation
general eqn:
RCH(OH)R’ + [O] –> RC=O R’ + H2O

22
Q

Describe oxidation of tertiary alcohols

A

Tertiary ROH cnt b oxidised
- oxidat n of alcohol involve cleavage of α C-H bond, absent in tertiary alcohols (α C-H is C bonded to OH)

23
Q

Describe special oxidation cases of carbonyl compounds

A

(methanol & ethane-1,2-diol)
- CH3OH + 2[O] – K2Cr2O7, H2SO4 (aq), heat –> HCOOH + H2O
- HCOOH + [O] –K2Cr2O7, H2SO4 (aq), prolonged heating –> CO2 + H2O
- CH3OH + 3[O] –KMnO4, H2SO4(aq), heat–> CO2 + H2O

CH2(OH)CH2(OH) + 2[O] – K2Cr2O7, H2SO4 (aq), heat –> O=C(OH)C(OH)=O (decompose to 2CO2, H2O w KMnO4) + 2H2O

CH2(OH)CH2(OH) + 5[O] – KMnO4, H2SO4 (aq), heat –> 2CO2 + 3H2O

24
Q

Describe chemical tests for alcohols

A

1.
test: add anhydrous PCl5 to compound
observ n: white fumes of HCl will b observed
general eqn: ROH + PCl5 –> RCl + POCl3 + HCl
type: Nu sub n

2.
test: heat compound w KMnO4 in H2SO4 (aq)
observ n: if 1°/2° alcohol present, decolour n of purple KMnO4 sol n is observed (3° ROH resistant to oxidat n)
General eqn:
1°: RCH2OH + 2[O] –> RCOOH + H2O
2°: RCH(OH)R’ +[O] –> RC=O R’ + H2O
type: oxidat n

  1. (Iodoform test)
    test add I2 in NaOH(aq) to compound, heat mix
    observ n: Pale yellow ppt of CHI3 will b observed
    general eqn: RCH(OH)-CH3/CH2I/CHI2/CI3 + 4I2 + 6NaOH –> RCOO-Na+ + CHI3 + 5NaI + 5H2O
25
Q

What are aryl alcohols?

A
  • aromatic cpd w -OH grp not directly bonded to benzene ring
    eg phenylmethanol, 2-phenylethanol
  • undergo similar rxn as aliphatic alcohols
  • can undergo E sub of benzene ring
26
Q

What are phenols?

A

Cpd w -OH gro attached direct to benzene ring hv phenol func grp

27
Q

How to name phenols?

A

Use ‘phenol’
eg 2-methylphenol, 4-chlorophenol

BUT, if higher priority gro present eg -RCOOH, -OH grp of phenol named as hydroxy
eg 4-hydroxybenzoic acid

28
Q

Describe physical properties of phenol

A
  • exist as crystalline solid at room temp (mp 34 deg C, bp 182 deg C)
    Bcos,
    High amt energy needed overcome strong H bond btw phenol molecule
  • caustic & poisonous
29
Q

Explain acidity of phenols when compared to water & ethanol

A

Relative acidity: ethanol < water < phenol
Bcos,
- phenoxide ion hv lp on O atom delocalised into benzene ring
- cause dispersal of -ve charge on phenoxide ion
- stabilises phenoxide ion
- acid strength increases

30
Q

Name reagent, condition & type of reaction of phenol and sodium

A

R&C: Na (or other reactive metals eg K)

Type: acid-metal displacemt

31
Q

Name reagent, condition and type of reaction of phenol and bases

A

R&C: NaOH(aq)/KOH(aq)

Type: Neutralisat n

NOTE: phenol no rxn w weak base eg Na2CO3, NaHCO3

32
Q

Do phenols react with carboxylic acids?

A

No
Bcos,
- phenol weaker nucleophile than alcool since lp e- on O atom delocalised into benzene ring
- cnt react w carboxylic acid form ester
- BUT, can react w acyl chlorides

33
Q

Name reagent, conditions and type of reaction of phenol and acyl chloride

A

R&C: RCOCl (specify acyl chloride if needed)
Type: Condensation

34
Q

Why sometimes phenol is first neutralised with eg NaOH(aq) before reacting with acyl chloride?

A
  • Neutralisat n forms phenoxide ion, stronger nucleophile than phenol
    => rate of rxn increases
35
Q

Why is phenol more susceptible to e-philic sub than benzene?

A
  • in phenol, lp e- on O atom delicalised into benzene ring
    => increase e- density in ring, so increase reactivity towards e-philes
  • thus, milder condit n needed for ES rxn of phenol
36
Q

Name reagent, conditions and type of reaction of phenol and dilute HNO3

A

R&C: HNO3(aq), r.t.p.

Type: E-philic sub n

NOTE: OH is 2, 4 directing, so 2 possible pdt
and, heating HNO3(aq) yields di-sub pdt 2,4-dinitrophenol

37
Q

Name reagent, conditions and type of reaction of phenol and concentrated HNO3

A

R&C: conc HNO3
type: e-philic sub n

*gives tri sub 2,4,6-trinitrophenol

38
Q

Name reagent, conditions, type of reaction AND observation of phenol and X2 in CCl4 (X= Cl/Br)

A

R&C: X2 in CCl4
type: e-philic sub n
observat n: (refer to data booklet for hexane colour) decolour n

39
Q

Name reagent, conditions, type of reaction AND observation of phenol and X2 (aq) (X= Cl/Br)

A

R&C: aq X2
Type rxn: e- sub n
observ n for Br2: Decolour n of orange aq Br2 & form n of white ppt 2,4,6-tribromophenol

NOTE: using X2(aq) means tri sub

40
Q

Describe chemical tests for phenol

A

1.
Test: Use neutral FeCl3 (aq)
Observ n: if phenol present, violet complex is observed
Type rxn: complex form n

  1. Test: add Br2(aq) to unknown compound
    Observ n: if phenol is present, decolour n of orange Br2(aq) & form n of white ppt (2,4,6-tribromophenol) are observed
    eqn:
    Phenol + 3Br2 (aq) —> 2,4,6-tribromophenol + 3HX
    type rxn: e- sub n
    NOTE:
    phenylamine (C6H5-NH2) oso give same observ n as phenol for test 2

La Chimie H2 (25 decks)

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