i.1 intro to organic compounds

7/29/2019 I.1 Intro to Organic Compounds

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William L Masterton

Cecile N. Hurleyhttp://academic.cengage.com/chemistry/masterton

Edward J. Neth University of Connecticut

Organic Chemistry

General, Organic, andBiochemistry, 8e

Bettelheim, Brown, Campbell, & Farrell
http://academic.cengage.com/chemistry/mastertonhttp://academic.cengage.com/chemistry/masterton


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Organic Chemistry

Organic chemistry: the study of the compounds of

carbon.

Organic compounds are made up of carbon and

only a few other elements.

chief among these are hydrogen, oxygen, andnitrogen

also present are sulfur, phosphorus, and halogens

(fluorine, chlorine, bromine, or iodine)


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Organic Chemistry

Why is organic chemistry a separate discipline within

chemistry?

Historical: scientists at one time believed that a vital

force present in living organisms was necessary to

produce an organic compound. The experiment of Whler in 1828 was the first in

a series of experiments that led to the demise of

the vital force theory.

NH4 Cl AgNCO H2 N-C-NH2

O

AgCl+ heat +

Ammoniumchloride

Silvercyanate

Urea Silverchloride


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Organic Chemistry

The sheer number of organic compounds

Chemists have discovered or made over 10million organic compounds and an estimated

100,000 new ones are discovered or made each

year.

By comparison, chemists have discovered or

made an estimated 1.7 million inorganic

compounds.

Thus, approximately 85% of all known compoundsare organic.


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Some organic chemicals

DNA

Essential oils

MedicinesActive Pharmaceutical Ingredients

Excipients

Materials

Fuels

Pigments


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Organic Chemistry

The link to biochemistry

Carbohydrates, lipids, proteins, enzymes, nucleicacids, hormones, vitamins, and almost all other

chemicals in living systems are organic

compounds.


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Organic Chemistry

Organic chemistry deals with compounds of carbon,

of which there are millions

Over 90% of all known compounds contain carbon

Carbon atoms bond to each other to a greater

extent than atoms of any other element Chains and rings may form


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Common Elements in Organic Chemistry

1. Organic compounds are molecular rather than ionic

2. Each carbon atom ordinarily forms four covalent

bonds

3. Carbon atoms may bond to atoms of other elements,

most often hydrogen, a halogen, oxygen, nitrogenand sulfur


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Organic Chemistry

a comparison of organic and inorganic compounds

Organic Comp ound s Inorgan ic Compounds

Bond ing is almost entirel y covalent

May be gases, liquids, or so lids

with low melting points (less

than 360C)Most are insoluble in water

Most are so luble in organ ic so lven ts

such as d iethy l ether, to luene , anddichloromethane

Aqu eous solutions do n otcondu ct el ectricity

Almost all burn

Reactions are usually slow

M ost have i onic bonds

M ost are solid s with high

melting points

M any are so luble i n water

Almost all are i nsoluble in

organic so lvents

Aqueous solutions conductelectricity

Very few burn

Reactions are o ften very fast


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Considerations in this Chapter

Hydrocarbons

Carbon and hydrogen only

Organic compounds containing N or O

Structural formulas

Isomerism

Organic Reaction


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Saturated Hydrocarbons: Alkanes

Formula: CnH2n+2

Simple alkanes (n = 1, 2, 3)

Carbons surrounded by four single bonds

sp3 hybrid orbitals Bond angles approximately 109.5


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n

1

2

3

4

5

6

MolecularFormula

CH4

C2H6

C3H8

C4H10

C5H12

C6H14

Structuralformula

H

C

H

CC

H

H

H

H

H

H

H

C

H

C

H

H

H

C

H

H

H

H

C

H

CC

H

H

C

H

H

H

H

C

H

CC

H

H

C

H

H

H

H

C

H

CC

H

H

C

H

H

H

H

H

H

H

H

H

H

C

H

H

H

H

H

C

H

H

C

H

H

H

Name

methane

ethane

propane

butane

pentane

hexane

Condensedstructuralformula

CH4

CH3CH3

CH3CH2CH3

CH3CH2CH2CH3

CH3CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH3


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Further members of the series

Heptane CH3CH2CH2CH2CH2CH2CH3

Octane CH3CH2CH2CH2CH2CH2CH2CH3

Nonane CH3CH2CH2CH2CH2CH2CH2CH2CH3

Decane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Undecane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

Dodecane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

Etc., etc.


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Table 22.1 Nomenclature of Alkanes


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Structural Isomers of Butane

Two different alkanes with the formula C4H10

Molecular view of alkanes Figure 22.1


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Figure 22.2 - Molecular Structures of Butane

Isomers


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Nomenclature

IUPAC naming schema

For straight chains, the name is based on a single

word

For branched chains, the name is derived from the

longest straight chain, with additions for branchpoints

Suffix is based on the longest chain

Prefix is numbered for the carbon where the branch is

located


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IUPAC Names for Isomers of Pentane


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Sources and Uses of Alkanes

Natural gas

80-90% methane

Remainder is C2H6, C3H3, and C4H10

Bottled gas

Compressed such that the gas inside is liquefied

Petroleum

Crude oil is the source of other hydrocarbons

Distillation separates the components Gasoline

Diesel fuel

Asphalt


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Figure 22.3 Bottled Gas


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Figure 22.4 Refining Petroleum


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Gasoline

Straight chain and branched isomers

Branched isomers burn more smoothly

Anti-knock compounds

Tetraethyl lead (C2H5)4Pb Not used in the US in decades

Ethyl alcohol (C2H5OH)

Currently widely used in gasoline


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Cycloalkanes

Alkanes can form rings rather than straight chains

These are called cycloalkanes

Contain two fewer hydrogens than chain alkanes


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Figure 22.5 - Molecular Structure of Cycloalkanes


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Unsaturated Hydrocarbons: Alkenes and Alkynes

Unsaturated compounds contain at least one

multiple bond

Alkenes contain double bond(s)

Each double bond replaces a pair of hydrogens

General formula is CnH2n Alkynes contain triple bond(s)

Each triple bond replaces two pairs of hydrogens

General formula is CnH2n-2


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Structures of Alkenes and Alkynes

Alkene

Alkyne


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Example 22.3


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Alkenes

The simplest alkene: ethene (common name, ethylene)

A double bond consists of a sigma and a pi bond

There is no rotation about the bond

The ideal bond angles are 120 Ethene is produced commercially in vast quantity

Used as a starting material for polyethylene

Also a plant hormone that ripens fruit


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Naming Alkenes

Alkenes are named as alkanes, with two exceptions

-ane is replaced byene

Where necessary, the number used to designate

the carbon of the double bond is made as small as

possible


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Example 22.4


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Alkynes

The name of an alkyne is derived from that of an

alkane, with the suffix changed fromane toyne Acetylene, C2H2, is the most common alkyne

(systematic name: ethyne)


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Acetylene

Acetylene is used as a welding gas

C2H2 (g) + O2 (g) CO2 (g) + H2O (l) H = -1300 kJ

Acetylene is thermodynamically unstable with

respect to decomposition into its elements

C2H2 (g)

2C (g) + H2 (g) G = -209.2 kJ at 25 C Because of the instability, acetylene is stored in a cylinder

packed with porous material as a solution in acetone

A ti H d b d D i ti


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Aromatic Hydrocarbons and Derivatives

Aromatic hydrocarbons (also called arenes)

Derived from benzene (C6H6)

Highly unsaturated

Differ in properties from alkenes

Each carbon forms three sigma bonds, one to ahydrogen atom and two to carbon atoms

The remaining electron pairs are spread over the

molecule


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Condensed Ring Structures

Fusion of benzene rings results in polycyclic

compounds


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Functional Groups

Many organic molecules contain functional groups

Functional group: an atom or group of atoms within amolecule that shows a characteristic set of

predictable physical and chemical properties.

Nonmetal atom Small group of atoms


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Functional Groups

Functional groups are important because

They undergo the same types of chemicalreactions no matter in which molecule they are

found.

To a large measure they determine the chemicaland physical properties of a molecule.

They are the units by which we divide organic

compounds into families.

They provide the basis on which we derive names

for organic compounds.


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Table 22.2


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Alcohols

Alcohols, R-OH

R is the alkyl group

-OH is the functional group


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Ethers

Ethers have the general structure R-O-R

The R groups may be the same or different

CH3-O-CH3, dimethyl ether

CH3-O-CH2CH3, methyl ethyl ether


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Alcohols and Ethers

Properties of alcohols and ethers

Alcohols have higher boiling points than ethers ofcomparable molar mass

The hydrogen bond strengthens the interaction of

alcohol molecules

Ethers cannot hydrogen bond

Alcohols of low molar mass are generally water-

soluble

Again, the hydrogen bond accounts for the solubility


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Table 22.3 Physical Properties


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Commercial Alcohols and Ethers

Methanol is prepared from synthesis gas

ZnO, Cr2O3

CO (g) + H2O (l) CH3OH250 atm, 350 C

Ethanol is formed from fermentation of sugar

Common name: grain alcohol

CH3CH2OH

C (C )


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Commercial Alcohols and Ethers, (Contd)

Alcohols with more than oneOH group

Diethyl ether C3CH2OCH2CH3

Ethers react with oxygen in air to form peroxides,

which are potent explosives

Ald h d d K


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Aldehydes and Ketones

The carbonyl group

In a ketone, there are alkyl groups

on either side of the carbonyl group

In an aldehyde, there is a hydrogen

on one side (at the end of the chain)

Properties of aldehydes are different from those of

ketones

C Ald h d d K t


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Common Aldehydes and Ketones

Acetone

Water soluble

Common solvent

Used in fingernail polish remover

Formaldehyde Used in a water solution as formalin

Preservative

Carcinogenic

A ti Ald h d


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Aromatic Aldehydes

Aromatic aldehydes are used as flavoring agents

and as odorants

E l 22 6


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Example 22.6

C b li A id d E t


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Carboxylic Acids and Esters

Carboxylic acid

Common carboxylic acids

A idit f C b li A id


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Acidity of Carboxylic Acids

RCOOH (aq) H+ (aq) + RCOO- (aq)

Strength varies from weak to strong

Trichloroacetic acid has Ka = 0.20

Strong acid

Used to remove warts Treatment of carboxylic acids with alkali metal

hydroxide (strong base) results in a sodium salt of

the acid

For long-chain acids, these are soaps

E t


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Esters

Reaction between a carboxylic acid and an alcohol

results in an ester

The reaction between acetic acid and methyl alcoholis typical of these reactions

Product is methyl acetate

T bl 22 4 P ti f E t


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Table 22.4 - Properties of Esters

A i


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Amines

Amines have the structure R-NH2

Primary amines have one alkyl group

CH3NH2, methylamine, is the simplest amine

Flammable gas

Unpleasant, fishy odor Weak base (Kb = 4 X 10

-4)

Reacts with strong acid

CH3NH2 (aq) + H+ (aq) CH3NH3

+ (aq)

Other amines have foul odors

Isomerism in Organic Compounds


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Isomerism in Organic Compounds

Isomers are distinctly different compounds, with the

same molecular formula Have different chemical and physical properties

Chain Structural Isomers


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Chain Structural Isomers

Consider the structural isomers of C5H12

One is linear and the other two are branched

Position Structural Isomers


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Position Structural Isomers

Consider the structure C4H8

Look at the position or location of the double bond

Structural Isomers with Functional Groups


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Structural Isomers with Functional Groups

Consider the structural isomers of C3H8O

Two are alcohols; the third is an ether

Example 22 9


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Example 22.9

Stereoisomers


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Stereoisomers

Types of stereoisomers

Conformational, Geometric and Optical

same

connectivity

Stereoisomers

Chiral

Enantiomers Dias tereomers

Constitutional Isomers

Cis-TransIsomers

with

stereocenters

without

stereocenters

Achiral

different

connectivity

Isomers


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Geometric Isomers: cis trans


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Geometric Isomers: cis-trans

Geometric isomerism arises where alkenes are

concerned There is no free rotation about the double bond

Consider C4H8

One pair of isomers is geometric cis when groups are on same side of double bond;

trans when on opposite sides

Example 22 10


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Example 22.10

Optical Isomers


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Optical Isomers

Optical isomers are possible when at least one

carbon is bonded to four different atoms or groups Non-superimposable mirror images

Consider your right and left hands

They are mirror images They are not superimposable on each other

Figure 22 11 Optical Isomers


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Figure 22.11 Optical Isomers

Terminology


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Terminology

A carbon with four different atoms or groups bonded

to it is called chiral The two different forms are called enantiomers

The carbon atom is the chiral center

Molecules may contain more than one chiralcenter, and there are more than two enantiomers

as a result

Example 22 11


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Example 22.11

Two Stereocenters


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Two Stereocenters

For a molecule with n stereocenters, the maximum

number of possible stereoisomers is 2n. We have already verified that, for a molecule with

one stereocenter, 21 = 2 stereoisomers (one pair

of enantiomers) are possible.

For a molecule with two stereocenters, a

maximum of 22 = 4 stereoisomers (two pair of

enantiomers) are possible.

For a molecule with three stereocenters, amaximum of 23 = 8 stereoisomers (four pairs of

enantiomers) are possible.

and so forth

Interaction of Enantiomers with Light


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Interaction of Enantiomers with Light

When plane polarized light is passed through a

sample of an enantiomer, the plane is rotated fromits original position

Optical isomerism

One isomer rotates right

One isomer rotates left

Figure 22 13


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Figure 22.13

Optical Activity


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Optical Activity

Dextrorotatory: clockwise rotation of the plane of

plane-polarized light. Levorotatory: counterclockwise rotation of the

plane of plane-polarized light.

Specific rotation: the observed rotation of anoptically active substance at a concentration of 1

g/mL in a sample tube 10 cm long.

DD

H3 CC

OHH

COOH

CH3

C

HO

H

COOH

[ ]

21= -2.6= +2.6

21

[ ]

(R)-(-)-Lactatic acid(S)-(+)-Lactic acid

Optical Inactivity


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Optical Inactivity

If both isomers are present in equal amounts, the

mixture is called racemic Offsets cancel and there is no net rotation

Mesocompounds- when there is internal mirrorimage, optical rotation will cancel out

Organic Reactions


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Organic Reactions

Organic reactions

Usually between molecules, not ions Solvents are often nonpolar

Four general types

Addition Elimination

Condensation

Substitution

Polymers


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Polymers

Polymers are large molecules

Made up of smaller units called monomers Chain of monomers can be thousands of units

long

Synthetic organic polymers Joined by addition orcondensation

Make up tires, cups, plates, fabrics

Natural polymers Cellulose, a polymeric carbohydrate

Proteins

Table 23.1 - Synthetic Addition Polymers


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Table 23.1 Synthetic Addition Polymers

i.1 intro to organic compounds

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