Phenol Flashcards

1
Q

Chemical properties of phenols

A
  1. Acidic
  2. Does not undergo nucleophilic sub.
  3. Stability depends on the groups present in a phenol
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2
Q

Why are phenols acidic?

A

Phenoxide ions (the conjugate base of phenols) are resonant stabilised. The p-p orbital overlap between unhybridised p orbital of O and pi electron cloud of benzene results in the delocalisation of lone pair of electrons on O into the benzene ring. This disperses the negative charge on O hence stabilising the phenoxide ion.
Thus the forward dissociation reaction of phenols to form phenoxide ions and H+ hence phenols are acidic

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3
Q

Why phenols do not undergo nu:sub

A

The lone pair of electrons on O delocalises into the benzene ring due to p-p orbital overlap. Hence the lone pair on O are less available to nu: attack.

Moreover since the C-O bond is strengthened and has partial double bond character which is harder to overcome

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4
Q

The stability of phenols depends on the groups they are attached to

A
  1. Electron withdrawing groups (NO2, Cl)
    - Electron withdrawing groups disperse the negative charge on O hence further stabilising the phenoxide ion
  2. Electron donating groups
    - Electron donating groups intensify the negative charge on O hence destabilising the phenoxide ion
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5
Q

Reactions

A
  1. Redox
    - Na(s) to from phenoxide Na+ and 1/2H2
  2. Acid base
    - NaOH(aq) from phenoxide Na+ and H2O
  3. Condensation (nu:sub)
    - Na(s), RCOCl, heat to form ester
    Na generates phenoxide ion which is more stronger nucleophile than phenol
  4. Electrophilic subs
    - Br2(aq)
    a) trisub 2,4,6, bromo phenol
    white ppt/orange Br2 decolourises
    - Br2 (aq) in CCl4(aq)
    b) monosub 2/4 bromo phenol
    orange-red decolourises
    c) HNO3(aq)
    monosub nitrophenol
    d) conc HNO3
    trisub nitrophenol, white ppt
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6
Q

Test for phenol

A

neutral FeCl3(aq)
- violet colouration observed

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