Organic Chemistry

Introduction

• Organic chemistry is a branch of chemistry that studies compound

based on carbon.• In particular it deals with hydrocarbons rather than metal

carbonates or oxides.• It was once thought that organic molecules could only be

made by living things and not in the lab, hence the name.

• Hydrocarbons are compounds that contain mostly H and C. Other common elements are oxygen, nitrogen and the halogens.

• Biochemistry can be thought of as a specialized branch of organic chemistry.

CARBON

• Hydrocarbons are a major source of energy in fuels and foods (petroleum, coal, natural gas, protein, carbohydrates, fats) and are the basis of drugs, materials (fabric, plastic), detergents, dyes and explosives.

• Carbon is in group 4 and always forms cova-lent bonds. As it has 4 valence electrons it will form 4 covalent bonds to com-plete its valence shell.

• In organic molecules, oxygen will always form 2 covalent bonds, hydrogen 1 bond, halogens 1 bond and nitrogen 3 bonds.

FUNCTIONAL GROUPS

• Carbon can form single and multiple bonds to other car-bons which result in different properties.

• When carbon forms bonds to other elements these make the compounds behave in cer-tain ways. These groups of atoms are called FUNCTIONAL GROUPS and de-termine the physical and chemical properties of an or-ganic compound.

Introduction to Hydrocarbons

• The simplest class of organic molecules is the hydrocarbons. • There are four major classes of hydrocarbons: alkanes,

alkenes, alkynes, and aromatics.

Alkanes contain only single bonds. • These compounds are also called saturated hydrocarbons

because they have the largest possible number of hydrogen atoms per carbon.

• Example: ethane (C2H6).

Alkenes contain at least one carbon-carbon double bond.

• They are also called olefins. • Example: ethene (C2H4).

Introduction to Hydrocarbons

• Alkynes contain a carbon-carbon triple bond. • Example: EThyne (C2H2)

• Aromatic hydrocarbons have carbon atoms connected in a planar ring structure. • The best known example is benzene (C6H6).

• Alkenes, alkynes and aromatic hydrocarbons are all examples of unsaturated hydrocarbons.

Hydrocarbons

Hydrocarbons

Names and Boiling points of alkanes

• The name of the alkane varies according to the number of C atoms present in the chain.

Homologous Series•W

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• A series of organic compounds with the same general formula, but that vary by a single –CH2 atom• Ex. Methane, Eth-

ane, Propane, etc.

Alkanes• We can make a table of members of a homologous

series of straight-chain alkanes. • Successive members differ by one CH2 unit.

• The names each end in -ane. • The prefix assigned indicates the number of carbon atoms.

• Example: CH4 is the alkane with a single carbon atom; it is called methane.

• The next member of the series is C2H6, with two carbon atoms; it is called ethane.

• The formulas for alkanes may be written in a notation called condensed structural formula. • This notation shows which atoms are bonded to one another

but does not require that we draw in all of the bonds. • Notice that each carbon in an alkane has four single bonds.

FUNCTIONAL GROUPS

• Organic compounds can be thought of as a carbon and hydrogen chain attached to one or more functional group.

• Carbon can form long chains that have the same functional group(s) and only differ by the number of carbons and hydrogen's present.

• This means the mass and properties vary in a regular and predictable manner.

• We call a group of compounds like this a HOMO-LOGOUS SERIES.

• CH3OH, C2H5OH, C3H7OH, C4H9OH• The General formula is CnH2n+1OH

HOMOLOGOUS SERIES

Homologous series can be thought of as families of organic compounds where:

• Successive compounds differ by a -CH2- unit.

• The compounds all have a general formula ex. CnH2n+2

• They have similar chemical properties.• Physical properties change in a regular

manner – as mass changes so do Vander Waals forces and sometimes the polarity of the molecules.

HOMOLOGOUS SERIES: PROPERTIES

Alkane Boiling Point °C

Methane, CH4 -164

Ethane, C2H6 -89

Propane, C3H8 -42

Butane, C4H10 -0.5

Pentane, C5H12 36

Hexane, C6H14 69

Heptane, C7H16 98

Octane, C8H18 125

• Note the trend in b.p. is predictable due to increase in Vander Waals’ forces with mass but it is not lin-ear – the increase in chain length is propor-tionally greater for the small chains.

• Other physical proper-ties that vary pre-dictably are density and viscosity.

FORMULAS, FORMULAE

• With organic compounds it’s important to know the difference between empirical, molecular, structural and full structural formulas.

• Empirical: simplest ratio of atoms ex. CH3 for ethane

• Molecular: actual number of atoms ex. C2H6

• Structural (condensed): shows overall struc-ture in one line ex. CH3CH2CH2COOH

• Full structural (displayed): shows every bond and atom ex.

• Skeletal Formula

R GROUP

• A group of CnH2n+1 can be represented by R.

• So an alcohol can be represented by R-OH.

• Benzene (C6H6) can be represented by: • Compounds containing benzene are

known as the aromatic compounds.

FUNCTIONAL GROUPS

Name Functional Group Prefix/suffix Example

Alkane None -ane CH4, methane

Alkene C=C -ene CH2=CH2, ethene

Alkyne C=C -yne CH=CH, ethyne

Alcohol -OH -anol (or hydroxy) CH3OH, methanol

Aldehyde -CHO -anal CH3CHO, ethanal

Ketone -CO -anone CH3COCH3, propanone

Carboxylic Acid -COOH -anoic acid CH3COOH, ethanoic acid

Halogenoalkane -X (F, Cl, Br or I) Halogeno- (fluoro ) CH3CH2Cl, chloroethane

Amine -NH2 -ylamine (or amino) CH3CH2NH2, ethylamine

Amide -CONH2 -anamide CH3CONH2, ethanamide

Ester R-CO-O-R’ Alkyl -alkanoate CH3COOCH3, methyl ethanoate

Nitrile -CN -anenitrile (or cyano-) CH3-CN, ethanenitrile (cyanomethane)

NOMENCLATURE

• Nomenclature means naming and there are IUPAC rules for naming organic compounds.

• The number of carbons determines the start of the name

Number of C atoms Stem Side Chain1 meth methyl2 eth ethyl3 prop propyl4 but butyl5 pent pentyl6 hex hexylBenzene ring benz phenyl

NAMING RULES

• Rule 1: Determine the longest continuous chain that provides the root name.

• Rule 2: If alkyl substituents are present as branched chains the name for the branch will b determined by the no. of carbon atoms the suffix will change from ‘–ane’ to ‘ –yl.’

• Rule 3: when no. the longest carbon chain the position of any substituent must be lower .

• When there are several different sub-stituents arrange them in alphabetical or-der prior to root name.

NAMING RULES

• Rule 5: Use a comma to separate numbers.

• Rule 6: Use a hyphen to separate the no. and letter.

• Rule 7: The no. of multiple substituents are shown by di, tri, tetra, pent pre-fixes.

• Rule 8: Successive words are merged in one word.

Prefixes for side chains

Side chain Prefix in IUPAC name Example

-CH3 Methyl- 2-methylpropane

-C2H5 Ethyl- 3 ethylpentane

-C3H7 Propyl- 4-propylheptane

-F,-Cl, -Br, -I Fluoro-, chloro-, bromo-, iodo-

Tetrachloromethane

-NH2 Amino- 2-aminoethanoic acid

ALKANES

• Alkanes contain hydrogen, carbon and all bonds are single.

• They follow the formula CnH2n+2 for ex.• CH4 is methane

• CH3-CH3 is called ethane

• CH3-CH2-CH3 is propane

• CH3CH2CH2CH3 is butane

ALKENES

• Alkenes also contain only C and H but con-tain at least 1 double bond.

• The formula is CnH2n.• The start of the name denotes the number

of carbons followed by a number to show which carbon the double bond is on fol-lowed by the ending –ene.

• CH2=CH-CH2-CH3 is but-1-ene.

• CH3-CH=CH-CH3 is but-2-ene.

ALKENES, ALKYNES, SATURATION

• Alkynes contain a C=C triple bond.

• Alkanes are SATURATED as they only have single bonds.

• Alkenes and alkynes are UNSATU-RATED as they contain multiple bonds. These bonds are stronger and mean that the molecules can react more.

• Alkenes are very important in the petrochemical industry as they are the starting place to make many other compounds.

Ester Functional group

• When the alkyl group of alcohol has re-placed the H of carboxylic acid.

C2H5COOH + HOCH3 → C2H5COOCH3

Methyl propanoate

CH3CH2CH2COOC2H5 Name it ?

Amide Functional group

They are acid derivatives when the –OH of acid is replaced by –NH2

RCOOH RCONH2

Propanamide N-methylpropanamide N,N-dimethyl-propanamide Primary amine Sec. Amine Tert. Amine

- OH

+ NH2

AMine functional group

• When H atom of ammonia are replaced by alkyl group then amines are formed.

NH3 -H +CH3 NH2CH3

NH2CH3 NH(CH3)2

NH(CH3)2 N(CH3)3

• Practice Questions