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Some history ,[object Object],[object Object],[object Object],[object Object]

בנזן - נוסחה אמפירית C 6 H 6 דוגמה לנוסחה אמפירית כזו בה היחס בין הפחמן למימן הוא 1:1 היא זו של האצטילן - C 2 H 2 HC=CH שוני גדול בין השניים - בניגוד לאצטילן בנזן לא מגיב ל : HCl, KMnO 4 , Br 2 , H 2 O/acid , אינו עובר תגובות של סיפוח שראינו באלקנים .

Kekul י and the Structure of Benzene

[object Object],Kekul י Formulation of Benzene H H H H H H

[object Object],Kekul י Formulation of Benzene H H H H H H H H H H H H

[object Object],Kekul י Formulation of Benzene H X X H H H H X X H H H

[object Object],Structure of Benzene Benzene has the shape of a regular hexagon.

All C—C bond distances = 140 pm 140 pm 140 pm 140 pm 140 pm 140 pm 140 pm

All C—C bond distances = 140 pm ,[object Object],140 pm 140 pm 140 pm 140 pm 140 pm 140 pm 146 pm 134 pm

The Stability of Benzene ,[object Object],[object Object]

[object Object],Thermochemical Measures of Stability  H°= – 208 kJ + 3H 2 Pt

Figure 11.2 (p 404) ,[object Object],120 kJ/mol 360 kJ/mol 3 x cyclohexene

Figure 11.2 (p 404) ,[object Object],[object Object],208 kJ/mol 360 kJ/mol 3 x cyclohexene

אנטלפית השריפה של בנזן חום השריפה מחושב - Kcal/mol -827 חום השריפה שמתקבל בפועל - 789 Kcal/mol - הפרש של 38 ק”קל למול

A Resonance Picture of Bonding in Benzene

[object Object],Resonance Formulation of Benzene H H H H H H H H H H H H

[object Object],Resonance Formulation of Benzene

Orbital Hybridization Model of Bonding in Benzene ,[object Object],Figure 11.3

Orbital Hybridization Model of Bonding in Benzene ,[object Object],[object Object],Figure 11.3

מושג הארומטיות ,[object Object],[object Object],[object Object],[object Object],[object Object]

תרכובות ארומטיות

Examples of Aromatic Hydrocarbons Benzene Toluene Naphthalene H H H H H H CH 3 H H H H H H H H H H H H H

11.8 Polycyclic Aromatic Hydrocarbons

[object Object],Naphthalene most stable Lewis structure; both rings correspond to Kekulé benzene

Anthracene and Phenanthrene Anthracene Phenanthrene resonance energy: 347 kJ/mol 381 kJ/mol

An Orbital Hybridization View of Bonding in Benzene

Substituted Derivatives of Benzene and Their Nomenclature

[object Object],General Points

Examples Bromobenzene tert -Butylbenzene Nitrobenzene NO 2 C(CH 3 ) 3 Br

[object Object],[object Object],[object Object],General Points

Ortho, Meta, and Para alternative locants for disubstituted derivatives of benzene 1,2 = ortho (abbreviated o -) 1,3 = meta (abbreviated m -) 1,4 = para (abbreviated p -)

Examples o -ethylnitrobenzene NO 2 CH 2 CH 3 m -dichlorobenzene (1-ethyl-2-nitrobenzene) (1,3-dichlorobenzene) Cl Cl

Table 11.1 (p 407) Certain monosubstituted derivatives of benzene have unique names

Table 11.1 (p 407) Benzaldehyde CH O

Table 11.1 (p 407) Benzoic acid COH O

Table 11.1 (p 407) Styrene CH 2 CH

Table 11.1 (p 407) Anisole OCH 3

Table 11.1 (p 407) Acetophenone CCH 3 O

Table 11.1 (p 407) Aniline NH 2

Easily confused names phenyl phenol benzyl OH CH 2 —

11.9 Physical Properties of Arenes

[object Object],[object Object],[object Object],[object Object],Physical Properties

Reactions of Arenes: Electrophilic Aromatic Substitution H E + E Y + H Y  +  –

12.2 Mechanistic Principles of Electrophilic Aromatic Substitution

מנגנון התמרה אלקטרופילית ב - Alkenes

Step 1: attack of electrophile on  -electron system of aromatic ring ,[object Object],[object Object],H H H H H H E + H H H H H H E +

Step 2: loss of a proton from the carbocation intermediate ,[object Object],[object Object],H H H E H H H + H H H H H H E +

H H H H H + E + H E H H H H + H + H H H H H H H E +

Electrophilic aromatic substitutions include: ,[object Object],[object Object],[object Object],[object Object],[object Object],H E + E Y + H Y  +  –

Table 12.1: Nitration of Benzene + + H 2 O H 2 SO 4 HO NO 2 Nitrobenzene (95%) H NO 2

Nitration of Benzene + + H 2 O H 2 SO 4 HO NO 2 Electrophile is nitronium ion H NO 2 O N O •• + •• • • • •

Where does nitronium ion come from? H 2 SO 4 + O N H O O + •• •• •• • • • • • • •• – O N H O O + •• •• •• • • • • •• – H + O N O •• + •• • • • • H O •• H ••

Step 1: attack of nitronium cation on  -electron system of aromatic ring H H H H H H NO 2 + H H H H H H NO 2 +

Step 2: loss of a proton from the carbocation intermediate H H H NO 2 H H H + H H H H H H NO 2 + מצבים רזונטביים

Table 12.1: Sulfonation of Benzene + + H 2 O heat HO SO 2 OH Benzenesulfonic acid (100%) H SO 2 OH

Sulfonation of Benzene + + H 2 O heat HO SO 2 OH Several electrophiles present: a major one is sulfur trioxide H SO 2 OH O S O O + •• •• •• • • • • • • •• –

Step 1: attack of sulfur trioxide on  -electron system of aromatic ring H H H H H H SO 3 H H H H H H SO 3 – +

Step 2: loss of a proton from the carbocation intermediate H H H SO 3 – H H H + H H H H H H SO 3 – +

Step 3: protonation of benzenesulfonate ion H 2 SO 4 H H H SO 3 – H H H H H SO 3 H H H

Table 12.1: Halogenation of Benzene + + H Br FeBr 3 Br 2 Bromobenzene (65-75%) H Br

Halogenation of Benzene + + H Br FeBr 3 Br 2 Electrophile is a Lewis acid-Lewis base complex between FeBr 3 and Br 2 . H Br

The Br 2 -FeBr 3 Complex ,[object Object],+ Lewis base Lewis acid FeBr 3 Complex • • Br Br • • •• •• •• •• Br Br • • •• •• •• •• FeBr 3 – +

Step 1: attack of Br 2 -FeBr 3 complex on  -electron system of aromatic ring H H H H H H Br Br FeBr 3 – + + FeBr 4 – H H H H H H Br +

Step 2: loss of a proton from the carbocation intermediate H H H Br H H H + H H H H H H Br +

Friedel-Crafts Alkylation of Benzene

Table 12.1: Friedel-Crafts Alkylation of Benzene + + H Cl AlCl 3 tert -Butylbenzene (60%) (CH 3 ) 3 C Cl H C(CH 3 ) 3

[object Object],Role of AlCl 3 (CH 3 ) 3 C Cl •• •• + AlCl 3 • • + (CH 3 ) 3 C Cl •• •• AlCl 3 –

Friedel-Crafts Alkylation of Benzene + + H Cl AlCl 3 Electrophile is tert -butyl cation (CH 3 ) 3 CCl H C(CH 3 ) 3 C CH 3 H 3 C H 3 C +

[object Object],Role of AlCl 3 (CH 3 ) 3 C Cl •• •• + AlCl 3 + (CH 3 ) 3 C + • • + (CH 3 ) 3 C Cl •• •• AlCl 3 – Cl •• •• AlCl 3 – • •

Step 1: attack of tert-butyl cation on  -electron system of aromatic ring H H H H H H H H H H H H C(CH 3 ) 3 + C(CH 3 ) 3 +

Step 2: loss of a proton from the carbocation intermediate H H H C(CH 3 ) 3 H H H + H H H H H H C(CH 3 ) 3 +

Friedel-Crafts Acylation of Benzene

Table 12.1: Friedel-Crafts Acylation of Benzene + + H Cl AlCl 3 1-Phenyl-1-propanone (88%) H O CH 3 CH 2 C Cl CCH 2 CH 3 O

Friedel-Crafts Acylation of Benzene + + H Cl AlCl 3 O CH 3 CH 2 CCl CCH 2 CH 3 O Electrophile is an acyl cation H •• CH 3 CH 2 C O • • + CH 3 CH 2 C O • • +

Step 1: attack of the acyl cation on  -electron system of aromatic ring H H H H H H H H H H H H + O CCH 2 CH 3 + O CCH 2 CH 3

Step 2: loss of a proton from the carbocation intermediate H H H H H H + H H H H H H + O CCH 2 CH 3 O CCH 2 CH 3

Reactions Related to Friedel-Crafts Alkylation ,[object Object],H 2 SO 4 + Cyclohexylbenzene (65-68%) H

Substituent Effects in Electrophilic Aromatic Substitution: הכנסת מתמיר שני לטבעת

הכנסת מתמיר שני לטבעת ,[object Object],[object Object],[object Object]

Table 12.2 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],Generalizations

[object Object],Electron-Releasing Groups OR such as —OH, and —OR are strongly activating

[object Object],Nitration of Phenol HNO 3 + 44% 56% OH OH NO 2 OH NO 2

[object Object],Bromination of Anisole Br 2 90% acetic acid OCH 3 OCH 3 Br

[object Object],Examples ERG = • • • • OH •• OR • • •• • • NH 2 • • NHR • • NR 2

מדוע קבוצות אלה גורמות לאקטיבציה ולהכוונה לעמדות ortho, para הסבר – שתי סיבות מולקולת האם מצבי הביניים לאחר כניסת המתמיר

Substituent Effects in Electrophilic Aromatic Substitution: Strongly Deactivating Substituents

[object Object],Many EWGs Have a Carbonyl Group Attached Directly to the Ring — EWG = — NO 2 — SO 3 H O — CH O — CR O — COH O — COR O — CCl — C N

הסיבות להכוונה לעמדת meta ודאקטיבציה

Nitration of Benzaldehyde HNO 3 75-84% H 2 SO 4 CH O CH O O 2 N

Problem 12.14(a); page 468 Cl 2 62% FeCl 3 Cl CCl O CCl O

Disulfonation of Benzene SO 3 90% H 2 SO 4 SO 3 H HO 3 S

Bromination of Nitrobenzene Br 2 60-75% Fe Br NO 2 NO 2

12.14 Substituent Effects in Electrophilic Aromatic Substitution: Halogens ,[object Object],גורמים לדאקטיבציה חלשה והכוונה לעמדות ortho, para

Nitration of Chlorobenzene ,[object Object],HNO 3 + + 69% 1% 30% H 2 SO 4 Cl Cl NO 2 Cl NO 2 Cl NO 2

[object Object],The Simplest Case AlCl 3 + CH 3 CH 3 CCH 3 99% O CH 3 COCCH 3 O CH 3 CH 3 O

[object Object],Another Straightforward Case CH 3 NO 2 Br 86-90% CH 3 NO 2 Br 2 Fe

Generalization ,[object Object]

[object Object],The Simplest Case Br 2 87% acetic acid strongly activating NHCH 3 Cl NHCH 3 Cl Br

[object Object],Steric effects control regioselectivity when electronic effects are similar 98% HNO 3 H 2 SO 4 CH 3 CH 3 NO 2 CH 3 CH 3

12.16 Regioselective Synthesis of Disubstituted Aromatic Compounds

Factors to Consider ,[object Object]

Synthesis of m-Bromoacetophenone ,[object Object],Br CCH 3 O CCH 3 O Br

Synthesis of m-Bromoacetophenone para meta Br CCH 3 O

Synthesis of m-Bromoacetophenone AlCl 3 Br 2 AlCl 3 CCH 3 O O CH 3 COCCH 3 O CCH 3 O Br

Factors to Consider ,[object Object],[object Object]

Synthesis of p-Nitrobenzoic Acid from Toluene ,[object Object],CH 3 CO 2 H NO 2 CH 3

Synthesis of p-Nitrobenzoic Acid from Toluene nitration gives m -nitrobenzoic acid oxidation gives p -nitrobenzoic acid CH 3 CO 2 H NO 2 CH 3

Synthesis of p-Nitrobenzoic Acid from Toluene HNO 3 H 2 SO 4 Na 2 Cr 2 O 7 , H 2 O H 2 SO 4 , heat CH 3 NO 2 CH 3 NO 2 CO 2 H

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