Benzene and Aromatic Compounds

Slides:



Advertisements
Similar presentations
Chapter 17 Benzene and Aromatic Compounds
Advertisements

CHEMISTRY 2600 Topic #7: Benzene and Its Reactions Spring 2008 Dr. Susan Lait.
Aromaticity hydrocarbons aliphaticaromatic alkanes alkenes alkynes.
1 Chapter 13 Unsaturated Hydrocarbons 13.7 Properties of Aromatic Compounds.
Benzene and Aromatic Compounds
By: Dr. Siham Lahsasni. BENZENE : Resonance description Later spectroscopic evidence showed all bond lengths in benzene to be equal and intermediate between.
Chapter 14 Aromatic Compounds. Benzene – a remarkable compound Discovered by Faraday 1825 Formula C6H6 Highly unsaturated, but remarkably stable Whole.
Learning Objectives  Understand the resonance description of structure of benzene  Understand the hybridization in benzene 
Elimination Reactions. Dehydrohalogenation (-HX) and Dehydration (-H 2 O) are the main types of elimination reactions.
245 Chapter 11: Arenes and Aromaticity 11.1: Benzene - C 6 H : Kekulé and the Structure of Benzene Kekule benzene: two forms are in rapid equilibrium.
L. Scheffler IB Chemistry 3-4. Lincoln H.S.
Aromaticity Dr. A.K.M. Shafiqul Islam
Aromatic Compounds. Lecture Outline Aromatic vs aliphatic compounds Aromatic vs aliphatic compounds Benzene Benzene Structure/ stability Structure/ stability.
Chapter 12: Unsaturated Hydrocarbons
1 (2 August 2002, Kansas) Police said an Olathe man was struck and killed by a train after his vehicle broke down on Interstate 35. His attempts at repairing.
Arenes Textbook p4-5.
Objectives To learn to name hydrocarbons with double and triple bonds
Benzene animations This resembles the ideas of Kekule who saw benzene as cyclohexatriene.
Aromatic Hydrocarbons Introduction Kekule proposed the structure of benzene Resonance Theory The Stability of Benzene The Criteria for Aromaticity—Hückel’s.
1 Aromatic Compounds Aromatic was used to described some fragrant compounds in early 19 th century but are now grouped by chemical behavior (unsaturated.
15. Benzene and Aromaticity
Chapter 15: Benzene and Aromaticity. 2 Aromatic Compounds Aromatic was used to described some fragrant compounds in early 19 th century –Not correct:
Benzene and the Concept of Aromaticity other representations: two equivalent resonance forms:
Structure of Alkenes Alkenes (and alkynes) are unsaturated hydrocarbons Alkenes have one or more double bonds The two bonds in a double bond are different:
Aromatic Compounds.
1 CH 15: Benzene and Aromaticity Renee Y. Becker Valencia Community College CHM 2211C.
Aromatic Compounds Chapter Chem 1. The expressing aromatic compounds came to mean benzene and derivatives of benzene. Structure of Benzene: Resonance.
Aromatic compounds Dr AKM Shafiqul Islam. hydrocarbons aliphaticaromatic alkanes alkenes alkynes Aromaticity.
Organic 2 Dr. Thoraya A.Farghaly.
1 Benzene and Aromatic Compounds. 2 Benzene (C 6 H 6 ) is the simplest aromatic hydrocarbon (or arene). Benzene has four degrees of unsaturation, making.

Aromatic compounds
PREPARATION OF CYCLOALKANES via:
Reactions of Arenes 1.
Name the homologous series
Chemistry Department, College of Science, King Saud University
Aromatic compounds 1.
Aromatic compounds
CH 15: Benzene and Aromaticity
1.3 AROMATIC HYDROCARBONS
Chapter 14 Aromatic Compounds
Chapter 14 Aromatic Compounds
Organic Chemistry, First Edition Janice Gorzynski Smith
Addition of HX to an Unsymmetrical Alkene
(2 August 2002, Kansas) Police said an Olathe man was struck and killed by a train after his vehicle broke down on Interstate 35. His attempts at repairing.
Aromatic compounds
Benzene and Aromatic Compounds
Aromatic Compounds.
15. Benzene and Aromaticity
Benzene & Aromatic Compounds
12/4/2018 CHEM 244 PRINCIPLES OF ORGANIC CHEMISTRY I FOR CHEMICAL ENGINEERING’ STUDENTS, COLLEGE OF ENGINEERING PRE-REQUISITES COURSE; CHEM 101 CREDIT.
CH 15: Benzene and Aromaticity
Electrophilic Aromatic Substitution (Aromatic compounds)
Chapter 14 Aromatic Compounds
Aromatic Compounds.
15. Benzene and Aromaticity
Fundamentals of Organic Chemistry
Benzene and Aromatic Compounds
Benzene and Aromatic Compounds
Fundamentals of Organic Chemistry
4/30/2019 CHEM 240 PRINCIPLES OF ORGANIC CHEMISTRY I FOR CHEMISTRY’ STUDENTS, COLLEGE OF SCIENCE PRE-REQUISITES COURSE; CHEM 101 CREDIT HOURS; 2 (2+0)
Aromaticity of Benzenoid and Non-benzenoid compounds
Aromatic Compounds.
Fundamentals of Organic Chemistry
Fundamentals of Organic Chemistry
Fundamentals of Organic Chemistry
Benzene and Aromaticity
Benzene and Aromatic Compounds
Fundamentals of Organic Chemistry
Fundamentals of Organic Chemistry
Presentation transcript:

Benzene and Aromatic Compounds Chem-160 4/6/2019 D rSeemal Jelani

The Structure of Benzene In benzene, the actual bond length (1.39 Å) is intermediate between the carbon—carbon single bond (1.53 Å) and the carbon—carbon double bond (1.34 Å). 4/6/2019 D rSeemal Jelani

Interesting Aromatic Compounds Benzene and toluene, the simplest aromatic hydrocarbons obtained from petroleum refining, are useful starting materials for synthetic polymers. They are also two of the components of the BTX mixture added to gasoline to boost octane ratings. Compounds containing two or more benzene rings that share carbon—carbon bonds are called polycyclic aromatic hydrocarbons (PAHs). Naphthalene, the simplest PAH, is the active ingredient in mothballs. 4/6/2019 D rSeemal Jelani

KMnO4 oxidation no reaction Br2/CCl4 addition HI H2/Ni reduction Reagent Cyclohexene Benzene KMnO4 oxidation no reaction Br2/CCl4 addition HI H2/Ni reduction 4/6/2019 D rSeemal Jelani

Benzene + 3 H2, Ni, room temp.  NR Benzene + 3 H2, Ni, 200oC, 1500 psi  cyclohexane Although highly unsaturated, benzene does not react like alkenes, dienes, cycloalkenes, or alkynes (addition reactions) rather it undergoes substitution reactions instead. 4/6/2019 D rSeemal Jelani

Freidel-Crafts alkylation C6H6 + RX, AlCl3  C6H5R + HX substitutions Reactions of benzene: Nitration C6H6 + HNO3, H2SO4  C6H5NO2 + H2O Sulfonation C6H6 + H2SO4, SO3  C6H5SO3H + H2O Halogenation C6H6 + X2, Fe  C6H5X + HX Freidel-Crafts alkylation C6H6 + RX, AlCl3  C6H5R + HX substitutions 4/6/2019 D rSeemal Jelani

The bonds in benzene are all equal and 1.39 Å e) From X-ray, all of the C—C bonds in benzene are the same length and intermediate in length between single and double bonds. C—C single bonds  1.50 Å C = C double bonds  1.34 Å The bonds in benzene are all equal and 1.39 Å but 1,3,5-cyclohexatriene has three double bonds and three single bonds! 4/6/2019 D rSeemal Jelani

Key Ideas on Benzene Unusually stable heat of hydrogenation 150 kJ/mol lower than a cyclic triene Planar hexagon: bond angles are 120° carbon–carbon bond lengths 139 pm Undergoes substitution not addition Resonance hybrid One more important factor is the number of electrons in the cyclic orbital 4/6/2019 D rSeemal Jelani

Aromaticity E Huckel (1931) Aromaticity is a property of certain molecules Chemistry would be similar to benzene Meet the following criteria Planar Mono cyclic system Conjugated pi system Contains 4n + 2  electrons Can apply rules to variety of compounds and determine aromatic nature. 4/6/2019 D rSeemal Jelani

4/6/2019 D rSeemal Jelani

4/6/2019 D rSeemal Jelani

Aromaticity and the 4n + 2 Rule Huckel’s rule, based on calculations – a planar cyclic molecule with alternating double and single bonds has aromatic stability if it has 4n+ 2  electrons (n is 0,1,2,3,4) For n=1: 4n+2 = 6 benzene is stable and the electrons are delocalized 4/6/2019 D rSeemal Jelani

Number of π electrons = 4 n + 2 6 = 4 n + 2 n = 1 For example, the benzene molecule, which has 3 π bonds or 6 π electrons, is aromatic. Number of π electrons = 4 n + 2 6 = 4 n + 2 n = 1 4/6/2019 D rSeemal Jelani

For n = 0, we get (4 × 0 + 2) = 2 For n = 1, we get (4 × 1 + 2) = 6 4/6/2019 D rSeemal Jelani

The letter “n” is not a characteristic of the molecule! Molecules that have the 3 characteristics listed above (cyclic, conjugated, flat) and have this number of π electrons [4n +2] will be aromatic. The letter “n” is not a characteristic of the molecule! 4/6/2019 D rSeemal Jelani