DAMIETTA UNIVERSITY CHEM-103: BASIC ORGANIC CHEMISTRY LECTURE

Transcription

1 DAMIETTA UNIVERSITY CHEM-103: BASIC ORGANIC CHEMISTRY LECTURE 8 Dr Ali El-Agamey

2 Nomenclature of Benzene Derivatives

3 Nomenclature of Benzene Derivatives To name a benzene ring with one substituent, name the substituent and add the word benzene.

4 Common Names of Benzene Derivatives Many monosubstituted benzenes have common names which you must also learn. =>

5 Common Names of Benzene Derivatives

6 There are three different ways that two groups can be attached to a benzene ring, so a prefix ortho, meta, or para can be used to designate the relative position of the two substituents. ortho-dibromobenzene or o-dibromobenzene or 1,2-dibromobenzene meta-dibromobenzene or m-dibromobenzene or 1,3-dibromobenzene para-dibromobenzene or p-dibromobenzene or 1,4-dibromobenzene

7 If the two groups on the benzene ring are different, alphabetize the names of the substituents preceding the word benzene. If one substituent is part of a common root, name the molecule as a derivative of that monosubstituted benzene. 1-Bromo-2-chlorobenzene 1-Fluoro-3-nitrobenzene 4-Bromotoluene 2-Nitrophenol

8 For three or more substituents on a benzene ring: 1. Number to give the lowest possible numbers around the ring. Do not use o, m, p method. 2. Alphabetize the substituent names. 3. When substituents are part of common roots, name the molecule as a derivative of that monosubstituted benzene. The substituent that comprises the common root is located at C1.

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10 The benzyl group, another common substituent that contains a benzene ring, differs from a phenyl group. Substituents derived from other substituted aromatic rings are collectively known as aryl groups.

11 When the benzene ring is a substituent of a parent chain, it is referred to as a phenyl group. The benzene ring is regarded as a substituent when the parent chain has greater than six carbons. The benzene ring is the parent when the longest alkyl chain substituent is six carbons or less A phenyl substituent (C 6 H 5 -) is often abbreviates as Ph- A C 6 H 5 -CH 2 - substitutent (phenylmethyl-) is often referred to as a benzyl group (Bn-) 11

12 Nomenclature of Benzene Derivatives

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14 Give the IUPAC name for each compound. PhCH(CH 3 ) 2 isopropylbenzene m-butylphenol 2-bromo-5-chlorotoluene

15 Which structure matches the given name? o-dichlorobenzene

16 4-chloro-1,2-diethylbenzene

17 What is the correct name for this compound? A) 3-Nitrotoluene B) 4-Nitromethylbenzene C) p-nitrotoluene D) (4,1)-Methylnitrobenzene

18 What is the correct name for this compound? A) 3,5-difluoroanisole B) Difluoromethoxybenzene C) 1,5-difluoro-3-methoxybenzene D) 1,3-difluoro-5-methyl-O-benzene

19 What is the correct name for this compound? A) 4-bromo-m-xylene. B) 1-bromo-2,4-dimethylbenzene. C) p-bromo-m-methyltoluene. D) o-bromo-m-methyltoluene.

20 What is the correct name? A) 1-fluoro-3-isopropyl-5-ethylbenzene B) 1-ethyl-3-isopropyl-5-fluorobenzene C) 1-ethyl-3-fluoro-5-isopropylbenzene D) 1-isopropyl-3-fluoro-5-ethylbenzene

21 Electrophilic aromatic substitution

22 Resonance Energy 22

23 Aromaticity Hückel s Rule

24 The Criteria for Aromaticity Hückel s Rule Four structural criteria must be satisfied for a compound to be aromatic. [1] A molecule must be cyclic. To be aromatic, each p orbital must overlap with p orbitals on adjacent atoms.

25 [2] A molecule must be planar. All adjacent p orbitals must be aligned so that the π electron density can be delocalized. Since cyclooctatetraene is non-planar, it is not aromatic, and it undergoes addition reactions just like those of other alkenes.

26 [3] A molecule must be completely conjugated. Aromatic compounds must have a p orbital on every atom.

27 [4] A molecule must satisfy Hückel s rule, and contain a particular number of π electrons. Hückel's rule: Benzene is aromatic and especially stable because it contains 6 π electrons. Cyclobutadiene is antiaromatic and especially unstable because it contains 4 π electrons.

28 Note that Hückel s rule refers to the number of π electrons, not the number of atoms in a particular ring.

29 p549e

30 Electrophilic aromatic substitution

31 Electrophilic aromatic substitution

32 Halogenation

33 Friedel Craft s Alkylation

34 -- p573c

35 Friedel Craft s Acylation

36 Nitration

37 p552b

38 p552c

39 Sulfonation

40 p552e

41 p554b

42 p554c

43 p555a

44 Reduction of the Nitro Group Treatment with zinc, tin, or iron in dilute acid will reduce the nitro to an amino group. This is the best method for adding an amino group to the ring. Chapter 17 44

45 Side-Chain Oxidation Alkylbenzenes are oxidized to benzoic acid by heating in basic KMnO 4 or heating in Na 2 Cr 2 O 7 / H 2 SO 4. The benzylic carbon will be oxidized to the carboxylic acid. Chapter 17 45

46 Clemmensen Reduction The Clemmensen reduction is a way to convert acylbenzenes to alkylbenzenes by treatment with aqueous HCl and amalgamated zinc. Chapter 17 46

47 Electrophilic Aromatic Substitution (5) Friedel-Crafts Acylation (1) Nitration (4) Friedel-Crafts Alkylation (3) Halogenation (2) Sulfonation

48 Homework: Complete the following scheme (1) (2) (3) (6) (7) (10) (11) (4) (5) (9) (8) (12) 48