chapter 1 introduction to organic chemistry: 1.1 organic compounds 1

Chapter 1 Introduction to Organic Chemistry:Chapter 1 Introduction to Organic Chemistry:

1.1 Organic Compounds

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Organic ChemistryOrganic Chemistry

An organic compound

• is a compound made from carbon atoms.• has one or more C atoms. • has many H atoms.• may also contain O, S, N, and halogens.

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Organic ChemistryOrganic Chemistry They are everywhere in our daily life

◦ foods, flavors and fragment◦ Medicines, toiletries and cosmetics◦ Plastics, films, fibers and resins◦ All other living organisms

Organic CompoundsOrganic Compounds

Typical organic compounds

• have covalent bonds.

• have low melting points.

• have low boiling points.

• are flammable.

• are soluble in nonpolar solvents.

• are not soluble in water.

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oil (organic) and water (inorganic)

Organic vs. InorganicOrganic vs. Inorganic

• Propane, C3H8, is an organic compound used as a fuel.

• NaCl, salt, is an inorganic compound composed of Na+ and Cl− ions.

Why is propane organic,but NaCl is not?

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ExamplesExamples

Identify each characteristic as most typical of compounds

that are 1) inorganic or 2) organic.

A. has a high melting point.

B. is not soluble in water.

C. has a formula CH3─CH2─CH3.

D. has a formula MgCl2.

E. burns easily in air.

F. has covalent bonds.

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1.2 Where do we obtain Organic 1.2 Where do we obtain Organic compounds?compounds?

Two principal ways: ◦ isolation from nature

is to extract and purify them from biological sources

◦ synthesis in the laboratory

Synthesis in the Laboratory Synthesis in the Laboratory Using different methods to made an organic compound or

develop their derivatives

Lewis StructuresLewis Structures represents how an atom’s valence electrons are

distributed in a molecule

Show the bonding involves (the maximum bonds can be made)

Try to achieve the noble gas configuration

The valence-shell electron-pair repulsion (VSEPR) model tell us the common angles about the carbon atoms

Writing Dot Lewis Structure: Rules Writing Dot Lewis Structure: Rules for multiple atomsfor multiple atoms Duet Rule: sharing of 2 electrons

◦ E.g H2 H : H

Octet Rule: sharing of 8 electrons◦ Carbon, oxygen, nitrogen and fluorine always obey

this rule in a stable molecule◦ E.g F2, O2

Bonding pair: two of which are shared with other atoms

Lone pair or nonbonding pair: those that are not used for bonding

1.3 How do We Write Structural 1.3 How do We Write Structural Formulas of Organic Compounds?Formulas of Organic Compounds?

A hydrogen molecule

• is stable with 2 electrons (helium).

• has a shared pair of electrons.

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Multiple BondsMultiple BondsIn a nitrogen molecule, N2,

• each N atom shares 3 electrons.• each N attains an octet.• the bond is a multiple bond called a triple

bond.• the name is the same as the element.

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Carbon Forms 4 Covalent BondsCarbon Forms 4 Covalent Bonds

Carbon normally forms four covalent bonds and has no unshared pairs of electrons

E.g In a CH4 (methane) molecule,

• 1 C atom shares electrons with 4 H atoms to attain an octet.

• each H atom shares 1 electron to become stable, like helium.

Bonding in Methyl Cation, the Bonding in Methyl Cation, the Methyl Radical, and the Methyl Methyl Radical, and the Methyl AnionAnion Not all carbon atoms form four bonds

C

carbocation

C

Carboanion

C

Carbo radical

General rules for Writing Dot Lewis structure General rules for Writing Dot Lewis structure involving N, O, H and Halogens involving N, O, H and Halogens

Nitrogen normally forms three covalent bonds and has one unshared pair of electrons

Oxygen normally forms two covalent bonds and has two unshared pairs of electrons

A halogen (fluorine, chlorine, bromine, and iodine) normally forms one covalent bond and has three unshared pairs of electrons

N

O

X

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Some Electronegativity Values for Group A Some Electronegativity Values for Group A ElementsElements

Low values

High values

` Electronegativity increases

` E

lectro

neg

ativ

ity d

ecre

ase

s

Copyright © 2009 by Pearson Education, Inc.

Polar Covalent Bonds: ElectronegativityPolar Covalent Bonds: Electronegativity

NaCl

HCl

Cl2

Writing Dot Lewis Structure with Writing Dot Lewis Structure with multiple center atomsmultiple center atoms Carbons will also be the center atom in the organic

molecule◦ -C-C-C- chains

Hydrogen is connected to carbon unless it’s an oxyacids (HClO, etc..) or Carbon has no more valence electrons to share

Order of increasing EN◦ (least) C N O F (most)

ExamplesExamples Write a Dot Lewis structure for the following atoms,

molecules and ions O N H2S CN-

CO32- C2H2

N2H4 CH2Cl2

Write a Dot Lewis structure for CH3COOH

Total Valence electron:H = 4 x1 = 4C = 2 x 4 = 8O = 2 x 6 = 12Total = 24

SkeletalC is less electro negative than OO does not bond to O

H C

H

H

C

O

O H

Bonding

C C O

O

H

H

H

H

Total e- = 24

bonding e - = 14

e- lef t = 10

C C O

O

H

H

H

H

Complete Octet

NOT :)) must form multiple bond

C C O

O

H

H

H

H

Total = 24 e-Bonding = 16Nonbonding = 8e- lef t = 0

Correct

ExampleExampleWrite a Dot Lewis Structure for

CH3NH2

VSEPR TheoryVSEPR Theory VSEPR theory proposes that the geometric

arrangement of terminal atoms, or groups of atoms about a central atom in a covalent compound, or charged ion, is determined solely by the repulsions between electron pairs present in the valence shell of the central atom

Common shape and angles◦ Linear (180o)◦ Tetrahedral (109.5o)◦ Trigonal planar (120o)

See table 1.2 page 5

ExamplesExamples Complete the following Dot Lewis structure by adding

the missing lone-pair then predict the bond angles

a.

b.

c.

C C

H

H Cl

H

H C

O

H

C NC

H

H

H

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Elements in Organic CompoundsElements in Organic Compounds

In organic molecules, carbon atoms bond • with four bonds.• mostly with H and other C atoms.• sometimes to O, N, S. • sometimes to halogens F, Cl, and Br.• Table 1.3 page 7

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Functional groups are• a characteristic feature of organic molecules that

behave in a predictable way. • composed of an atom or group of atoms. • groups that replace a hydrogen atom in the

corresponding alkane.• a way to classify families of organic compounds.

Functional GroupsFunctional Groups

AlcoholAlcoholAn alcohol

contains the hydroxyl (-OH) functional group.R-OH

R C

R

R

O H

Functional group

R = H or Carbon group (alkyl)

H3C C

H

H

O H

H3C C

CH3

H

O H

H3C C

CH3

CH3

O H

1o alcohol

2o alcohol

3o alcohol

Types of Alcohol

Writing structural formulas of Writing structural formulas of AlcoholAlcohol

CH4OMolecular formula

CH3OHCondensed formula

C

H

OH

H

H

Structural formualMethanol

Writing structural Formulas of Writing structural Formulas of AlcoholsAlcohols Draw Lewis structure and condensed structural

formulas for the four alcohol with molecular formula C4H10O. Classify each alcohol as primary, secondary or tertiary. ◦ Hints: Consider the connectivity of the four carbon

atoms; they can be bonded either four in a chain or three in a chain with the fourth carbon as a branch on the middle carbon. Then consider which carbon should connect to OH with having the same molecule

AminesAmines

In amines, the functional group is a nitrogen atom. RNH2, R2NH or R3N

H3C N

H

H Methylamine

1o amine

H3C N

CH3

H

H3C N

CH3

CH3

Dimethylamine

2o amine

Trimethylamine

3o amine

N

ExamplesExamples Draw structural formulas of the three secondary

amines with the molecular formula C4H11N

Ketone and AldehydeKetone and Aldehyde Aldehyde contains a carbonyl group bonded to a

hydrogen Ketone contains a carbonyl group bonded to two

carbon atoms

O

CR H

AldehydeR = CH3 or anyhydrocarbons

O

CR1 R2

KetoneR = CH3 or any hydrocarbons

Carboxylic AcidsCarboxylic Acids

Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group.

–COOH

O ║

— C—OH

ExamplesExamples Draw condensed structural formulas for the two

carboxylic acids with molecular formula C4H8O2

Carboxylic estersCarboxylic esters An ester contains the carboxyl group between

carbon atoms.

–COOR or –CO2R

C

O

O C

Functional group

ExamplesExamples Draw structural formulas for the four esters with the

molecular formula C4H8O2

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Learning CheckLearning CheckClassify each of the following as: alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, or amide.

1) CH3─CH2─CH2─OH

2) CH3─O─CH2─CH3

3) CH3─CH2─NH2

O O ║ ║

4) CH3─C─OH 5) CH3─C─O─CH3

ExamplesExamples Consider the formula C4H8O2. Write the structural

formula for this molecular formula with ◦ A carboxyl group◦ Ketone group and a 2o alcohol group◦ An aldehyde and a 3o alcohol group◦ A carbon-carbon double bond and a 1o alcohol