Lecture #25 (Chapter 21)

Lecture #25 (Chapter 21) - Phenols and Aryl Halides...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Phenols and Aryl Halides Nucleophilic Aromatic Substitution Phenols Phenols have the hydroxyl group attached to a benzene ring. The name is derived from the aryl group name by dropping the "yl" in phenyl and adding "ol." Substituted phenols are named by the usual positional rules used for substituted benzenes. OH phenol OH p-bromophenol (4-bromophenol) Br OH Cl NO 2 2-chloro-4-nitrophenol
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Some Important Phenols and their Common Names Some Naturally Occurring Phenols CH 3 OH o-cresol 2-methylphenol CH 3 OH p-cresol 4-methylphenol OH OH hydroquinone 1,4-benzenediol HO CH 2 CHCO 2 - NH 3 + tyrosine an aminoacid in proteins HO CH 2 CH 2 NH 2 dopamine N HO CH 2 CH 2 NH 2 H serotonin neurotransmitters CO 2 H OH salicylic acid CO 2 H OCCH 3 O = O-acetylsalicylic acid aspirin
Background image of page 2
Synthesis of Phenols Phenols are prepared by the hydrolysis of arenediazonium salts: Ar-NH 2 [HONO] HX ArN 2 X - + Cu 2 O Cu 2+ , H 2 O Ar-OH Substituted phenols may be prepared by this procedure: NH 2 Br [HONO] HCl diazotization N 2 Cl - Br + Cu 2 O Cu(NO 3 ) 2 , H 2 O hydrolysis OH Br p-bromophenol (95%)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Phenols as Acids Phenols are much more acidic than alcohols, but are weaker acids than carboxylic acids. RCO 2 H ArO H RO H pK a 4-5 ~10 ~18 These acidities are explained in terms of the different stabilities of the conjugate bases (A: - ) of the acids (HA) that influence the equilibrium: HA + H 2 O H 3 O + + A: - K a K a = [H 3 O + ] [A: - ] [HA] An increase in the stability of A: - drives the equilibrium more to the right increasing the magnitude of K a .
Background image of page 4
An Example: Cyclohexanol and Phenol Phenol is a much stronger acid than cyclohexanol. This difference in acidity is understandable in terms of the
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 16

Lecture #25 (Chapter 21) - Phenols and Aryl Halides...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online