Chapter 1. L1. Structure & Bonding

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Organic Chemistry

Fall, 2011 by Dr.Isam Al Naser

Credits: 2 hoursClass schedule

: San (11-13,30) section1.,Tus (11-13,30)section2

Class room:6038

Room number: 7234Office hours: Mon (09-12)

Wed (09-11), (13-15)



Lecture & Assignment Schedule (NEW) ExamsTopics to be coveredDateWeek

Introduction to the Study of Organic

Chemistry

29-03/10 1

Introduction to the Study of Organic

Chemistry

06-10/10 2

Polar covalent bonds13-17./10 3

Alkanes and their stereochemistry20-24/10 4

Radical, Reaction of Alkanes27-31/10 5

Cycloalkanes and ther stereochemistry

03-07/11 6

Alkenes :structure and reactivity10-14/11 7

Mid Exa

Mid Exa

17-21/11 8

Alkenes: reactions and synthesis24-28/11 9

Alkynes

01-05/12 10

stereochemistrys08-12/12 11

reactions of alky halides

15-19/12 12

reactions of alky halides

22-26/12 13

Alcohols and phenols29-02/13 14

Ethers and Epoxides

05-09/13 15

Final Exa Final Exa12-23/1316



Text Book

“ Organic Chemistry” 7th Edition,

(Brooks/Cole Publishing Company)

2008

by

Authors John Mc MurryISBN :978-1-4080-2052-4



Grading

: 15%

:35%

:50%



Chapter 1 Structure & Bonding

Organic chemistry is the study of the compounds of carbon. Includes biological molecules, drugs, solvents,

dyes,food additivives,pesticides.. Does not include metal salts and materials

(inorganic)



Organic chemistry ,study of carbon compounds

why is carbon special?

-90% of more than 30 million chemical compoundscontain carbon.-Examination of carbon in periodic table answerssome of these questions.-Carbon is group 4A element, it can share 4 valence

electrons and form 4 covalent bonds.



1.1 Atomic Structure

Atom: (2x10-10 m) Nucleus

• Protons (+) 10-14 ~ 10-15 m

• neutrons

Electrons (-) 10-10 m

Shell: A region of space around anucleuses Where electrons arefound.

Orbital: A region of space wherean electron or pair of

electron,spend90-95%fo time.

Diameter2 10-10 m (200 picometers (pm)) [the unit angstrom (Å)

is 10-10 m = 100 pm]



Atomic Number and Atomic Mass

The atomic number (Z ) is the number of protonsin the atom's nucleus H=1,C=6,P=15

The mass number ( A) is the number of protonsplus neutrons H=1,008 C=12,011 P=30,974

Isotopes are atoms with the same atomicnumber but different mass numbers ,that havedifferent numbers of neutrons



Shapes of Atomic Orbitals for Electrons

Four different kinds of orbitals for electronsbased on those derived for a hydrogen atom Denoted s, p, d , and f s and p orbitals most important in organic and

biological chemistry s orbitals: spherical, nucleus at center p orbitals: dumbbell-shaped, nucleus at

middle d orbitals: elongated dumbbell-shaped,

nucleus at center



Orbitals and Shells part 1

Orbitals are grouped in shells of increasingsize and energy

Different shells contain different numbers andkinds of orbitals

Each orbital can be occupied by two electrons



1.2 Electron Configuration of Atoms

Ground-state electron configuration Rules 1-3 at page 4

See Table 1.1 as examples



1.3 Chemical Bonding Theory

2D to 3D Tetrahedral carbon atom



1.4 The Nature of ChemicalBonds

Ionic Bonds Bond between ions due to the

electrostatic attraction : NaCl

Covalent Bonds Bonds formed by sharing electrons Lewis structures (electron-dot) Nonbonding electrons (lone-pair

electrons)



.Bonds

Lewis structures



Number of covalent bonds



Kekulé strutures (line-bond structure)•Table 1.2

1.4 The Nature of ChemicalBonds



1.5 The Nature of Chemical Bonds: ValenceBond Theory

Covalent bond forms when two atoms approach each otherclosely so that a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom

-Two models to describe covalent bonding.Valence bond theory, Molecular orbital theory

Valence Bond Theory: Electrons are paired in the overlapping orbitals and are

attracted to nuclei of both atoms H–H bond results from the overlap of two singly occupied

hydrogen 1s orbitals

H-H bond is cylindrically symmetrical , sigma ( ) bond



Bond Energy

Reaction 2 H· H2 releases 436 kJ/mol Product has 436 kJ/mol less energy than two

atoms: H–H has bond strength of 436 kJ/mol.(1 kJ = 0.2390 kcal; 1 kcal = 4.184 kJ)



Bond Length

Distance betweennuclei that leads tomaximum stability

If too close, they

repel because bothare positively charged If too far apart,

bonding is weak



1.5 Forming Covalent Bonds

Valence Bond Theory• Overlapping of two atomic orbital.

Bond strength• energy

Bond length• distance



1.5 Forming Covalent Bonds

Molecular orbitals (MO)There are two ways forthe orbital combinationto occur-an additive way

and a subtractive way .The additive way leds toformation of a MO thatis lower in energy and

roughly egg-shaped .The subtractive wayleads to formation of aMO that is higher inenergy and has a nodebetween nuclei

MO has a specific size,shape and energy exa.H2



1.6 Hybridization sp3 Orbitals and theStructure of Methane

Carbon has 4 valence electrons (2s2 2 p2) In CH4, all C–H bonds are identical (tetrahedral) sp3 hybrid orbitals: s orbital and three p orbitals combine to

form four equivalent, unsymmetrical, tetrahedral orbitals(sppp = sp3), Pauling (1931)



The Structure of Methane

sp3 orbitals on C overlap with 1s orbitals on 4 Hatoms to form four identical C-H bonds

Each C–H bond has a strength of 436 (438) kJ/moland length of 109 pm

Bond angle: each H–C–H is 109.5°

, the tetrahedral angle.



Ethane:CH3-CH3

Two C’s bond to eachother by s overlap of an sp3 orbital fromeach

Three sp3 orbitals on

each C overlap with H1s orbitals to form sixC–H bonds

C–H bond strength inethane 423 kJ/mol

C–C bond is 154 pmlong and strength is376 kJ/mol

All bond angles of ethane are tetrahedral



1.8 Double and Triple Bonds

Ethylene



sp2 hybrid orbitals: 2s orbital combineswith two 2 p orbitals, giving 3 orbitals (spp =sp2). This results in a double bond.

sp

2

orbitals are in a plane with120°

angles Remaining p orbital is perpendicular to theplane

Ethylene C2H4

s bond P bond

1.8 sp2 Orbitals and the Structure of Ethylene



H atoms form s bonds with four sp2 orbitals H–C–H and H–C–C bond angles of about 120° C–C double bond in ethylene shorter and stronger

than single bond in ethane

Ethylene C=C bond length 134 pm (C–C 154 pm)

Structure of Ethylene

1 9 sp Or ita s an t e Structure o C H



1.9 sp Or ita s an t e Structure oAcetylene

C2H2

One s-bond & two p-

bonds

C-C a triple bond sharing six electrons Carbon 2s orbital hybridizes with a single p

orbital giving two sp hybrids two p orbitals remain unchanged

sp orbitals are linear, 180° apart on x -axis Two p orbitals are perpendicular on the y -axis

and the z -axis



Orbitals of Acetylene

Two sp hybrid orbitals from each C form sp–sp s bond

p z orbitals from each C form a p z – p z p bond bysideways overlap and py orbitals overlap

similarly



Bonding in Acetylene

Sharing of six electrons forms C C

Two sp orbitals form s bonds with hydrogens



Elements other than C can have hybridized orbitals H–N–H bond angle in ammonia (NH3) 107.1° C-N-H bond angle is 110.3 ° N’s orbitals (sppp) hybridize to form four sp3 orbitals

One sp3 orbital is occupied by two nonbonding electrons, andother three sp3 orbitals have one electron each, forming bondsto H and CH3.

1.10 Hybridization of Nitrogen and Oxygen



33

1.12 Drawing Structures

Drawing every bond in organic moleculecan become tedious.

Several shorthand methods have been

developed to write structures. Condensed structures don’t have C-H or

C-C single bonds shown..

e.g.



Different compounds having the same molecular formula arecalled isomers

When the group of atoms that make up the molecules of different isomers are bonded together in fundamentallydifferent ways, we refer to such compounds as constitutionalisomers.

There are seven constitutional isomers of C4H10O, andstructural formulas for these are drawn in the following table.

There are no double or triple bonds and no rings in any of these structures.. Note that each of the carbon atoms isbonded to four other atoms, and is saturated with bondingpartners.

S l F l f C H O I



Structural Formulas for C4H10O Isomers Kekulé Formula Condensed Formula Shorthand Formula

Chapter 1. L1. Structure & Bonding

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