Introduction to Organic Chemistry Chapter-4 Introduction to Organic Chemistry

What is Organic Chemistry? It is defined as the study of hydrocarbons (compounds of hydrogen and carbon) and their derivatives 1.5 million Inorganic Compounds 7 million Organic Compounds

Organic Chemistry Carbon Compounds Organic Compounds Inorganic Compounds CO2 CO XCN XCO3 Hydrocarbons & Derivatives X=Metal

Animal and plant matter, Foods, Organic Chemistry We are enjoying the gifts of organic compounds directly or indirectly in our daily life such as Animal and plant matter, Foods, Fertilizers, Pharmaceuticals, Plastics, Cosmetics, Clothing, Detergents etc..

Organic Chemistry Fertilizers Detergents Vegetables Organic compounds Clothing Foods Cosmetics Plastics Medicine

General characteristics of organic compounds Covalent compounds. Contain 2 or more elements: C, H, O, N, S, P. Vast numbers of different compounds. Why? Ability to form long chains and rings Catenation 6

Covalent bond Single covalent bond F Lone pairs Lone pairs

Covalent bond lone pairs F single covalent bond

Catenation

Hydrocarbon Hydrocarbons are the simplest organic molecules. They contain only carbon and hydrogen.

Hydrocarbons

Classification of Hydrocarbons

Hydrocarbons Alkanes Alkenes Alkynes Arenes Simplest Methane, ethane, propane 13

Alkanes are the simplest type of Hydrocarbons

Names and Formulas for Some Common Hydrocarbons

The first 10 straight chain alkane

Methane Sp3 hybridized carbon 4 equivalent C-H bonds (s-bonds) All purely single bonds are called s-bonds

The Molecular Structure of Methane

Structure of Ethane

The Structures of Propane and Butane

Normal Butane and Iso Butane

-H Alkane Alkyl radical -H CH4 -CH3 When a hydrogen atom is removed from an alkane the remaining group of atoms is called alkyl group or alkyl radical. -H Alkane Alkyl radical -H CH4 -CH3

Alkyl group -H -H -H Methane CH4 CH3 Methyl Ethane C2H6 C2H5 Ethyl Propane C3H8 C3H7 Propyl

Functional group An atom or a group of atoms which impart characteristics properties to a compound is called Functional group.

Functional group

Homologous series A series of compounds of similar properties whose molecular formula differ by CH2 between adjacent members of the series

Homologous series The members show regular changes in properties n Molecular formula Name 1 4 CH4 Methane 2 6 C2 H6 Ethane 3 8 C3 H8 Propane 10 C4 H10 Butane 5 12 C5 H12 Pentane 14 C6 H14 Hexane 7 16 C7 H16 Heptane 18 C8 H18 Octane 9 20 C9 H20 Nonane 22 C10 H22 Decane As the # C-atoms ↑: reactivity ↓ mp ↑ bp ↑ d ↑ solubility ↓ The first 10 members of the alkanes (CnH2n+2)

Homologous series Formula Alkanes Cn H2n+2 Alkenes Cn H2n Alkynes Alcohols Cn H2n+1 OH Alkyl halides Cn H2n+1 X (X= F, Cl, Br, I) Homologous series Formula

Homologous series Formula Aldehydes Cn H2n+1CH O Ketones C nH2n CO Carboxylic acids Cn H2n+1 CO2 H Amides Cn H2n+1 CONH2 Amines Cn H2n+1 NH2 Homologous series Formula

Saturated hydrocarbons Unsaturated hydrocarbons Single bond Double bond Triple bond Alkanes Alkenes & Alkynes Substitution rxn Addition rxn

Which of the following compounds is saturated and which is unsaturated 37

Chemical formula Structural formula Molecular formula 38

Molecular formula Gives the numbers of each atom in a molecule Ethane C2H6

Shows, in 2-dimensions,exactly how the atoms are bonded to each other Structural formula Shows, in 2-dimensions,exactly how the atoms are bonded to each other

Examples Structural formula Molecular formula Methane Ethane Propane CH4 C2H6 C3H8

Examples Molecular formula Structural formula C4H10 C2H6O

Chemical formula Write down the molecular and structural formulae of the first six alkanes.

Isomerism

Isomerism Different molecules have the same molecular formula but different structural formula Isomers Different physical & chemical properties 45

Examples Molecular formula Structural formula C4H10 46

Examples Molecular formula C2H6O Structural formula

Types of Isomerism

Chain Isomerism or Skeletal Isomerism Compounds having same molecular formula but different carbon chain or carbon skeleton are called chain isomers and this phenomena is known as chain isomerism “This type of isomers differ only in the structure of their carbon chains or skeletons” 49

For example The molecular formula C5H12 , represents three isomeric alkanes differing only in structure of their carbon chains:

n-pentane C H

2-methylbutane H CH3 C C C C

2,2-dimethylpropane C H CH3

Position Isomerism Compounds having the same molecular formula but differ in the relative position of their functional group or the position of their double or triple bonds are called position Isomer . 54

Position Isomerism 1-Chlorobutane 2-Chlorobutane Molecular formula C4H9Cl represents two isomers in which the relative position of Cl is different, but they have the same carbon skeleton. CH3 - CH2 - CH2 - CH2-Cl 1-Chlorobutane Cl – 2-Chlorobutane CH3 - CH2 - CH – CH3

Position Isomerism Butan-1-ol Butan-2-ol CH3 - CH2 - CH2 - CH2-OH

position Isomer

This isomerism is common in two types of Functional Group Isomerism Compounds having the same molecular formula but different functional groups are called functional groups isomers This isomerism is common in two types of compounds: Ethers Alcohols

functional groups isomers

One of these is an ether and the other is an alcohol. Example The molecular formula C2H6O has at least two isomers which have different functional groups. One of these is an ether and the other is an alcohol. Ethers Alcohols

Aldehydes & Ketones

Molecular formula C3H6O represents one aldehyde and one ketone as Example Molecular formula C3H6O represents one aldehyde and one ketone as CHO CH3CH2 ketone Aldehyde

Metamerism

This isomerism is exhibited by ethers and amines. In this type of isomerism different alkyl groups are attached to the same polyvalent atom, such as O or N. This isomerism is exhibited by ethers and amines.

Molecular formula C4H10O represents three different ethers. Example Molecular formula C4H10O represents three different ethers. CH3-CH2-O-CH2-CH3 CH3-O-CH2-CH2-CH3 Diethyl ether Methyl Propyl ether

Classification of Carbon Atoms Primary Carbon Secondary Carbon Quaternary Carbon Tertiary Carbon

to one other carbon atom to two other carbon atoms Secondary Carbon Primary Carbon A carbon atom attached A carbon atom attached to one other carbon atom to two other carbon atoms

Quaternary Carbon Tertiary Carbon A carbon atom attached to four other carbon atoms A carbon atom attached to three other carbon atoms Quaternary Carbon Tertiary Carbon

Classification of carbon atoms

Organic Nomenclature

Common or Trivial System

This method of nomenclature was used before 1892. In this system of nomenclature, the compounds were named on the basis of their history, such as source of origin etc.

IUPAC SYSTEM

A method known as the Geneva system was suggested in 1892 by the International Chemical Congress at Geneva for naming organic compounds.

Later the International Union of Chemistry at Liege (Belgium) developed it into IUPAC system of nomenclature in 1930. In 1958, the IUPAC system was modified by the International Union of Pure and Applied Chemistry (IUPAC) into the present day IUPAC system of nomenclature.  

Rules for naming alkanes

Rule 1: Selection of longest continuous chain of carbon atoms as the parent name of the hydrocarbon. butane The longest continuous chain has four carbon atoms, thus the compound is named as butane.

Rule 2: Number the carbon atoms in the longest continuous chain in such a way as to give lowest possible number to carbons atoms carrying substituent's. CH3 CH CH2 1 2 3 4 5 2-methylpentane

CH3 CH CH2 5 4 3 2 1 4-methylpentane

Incorrect numbering Correct numbering

The attached group is located on carbon 2 of the chain, and it is a Rule 3: Name the substituent. Indicate its position by the number of the carbon atom to which it is attached. The attached group is located on carbon 2 of the chain, and it is a methyl group

The whole name is written as one word. Rule 4: Prefix the position number and name of the substituent onto the parent name. The whole name is written as one word. Notice that the number and name of the substituent are separated by a hyphen.

2-Methylbutane 2- Butane Methyl Attached alkyl group Longest chain Position of alkyl group 2-Methylbutane

Rule 5: If identical substituent's are present more than once in the molecule, then use prefixes di- tri-tetra-,penta-, etc.

Position of each substituent is indicated by a separate number. Rule 6: Position of each substituent is indicated by a separate number.

Rule 7: When two or more different substituent's are present, their names are arranges in alphabetic order and added to the name of the parent alkane, again as one word.

CH3 CH2 CH 1 2 3 4 5 6 7 4-methylheptane

Nomenclature guideline

Step-by-step procedure to write the IUPAC names from structural formula.

Step 1 Identify the longest chain. In this example, the longest chain contains seven carbons. the seven-carbon chain is heptane.

Step 2 Number the chain. The chain is numbered from left to right. This gives the lowest numbers to the attached alkyl groups.

Step 3 Identify the alkyl groups. There are two methyl groups at C-2 and C-3. There is one ethyl group at C-4

Step 4 Write the IUPAC name: In this case the IUPAC name is 4-Ethyl-2,3-dimethylheptane

Always remember

Numbers are separated from each other by commas; Numbers are separated from names by hyphens; Prefixes di-, tri-, are not taken into account in alphabetizing substituent names.

Structural formulas from the IUPAC names

Consider the following IUPAC name: Step-by-step procedure to draw structural formulas from the IUPAC names. Consider the following IUPAC name: 3,3-Diethyl-5-methyldecane

Step1 Draw a decane skeleton and number it.

Step 2 Attach two ethyl groups at C-3 C2H5 C2H5

Step 3: Attach a methyl group at C.5 CH3

Supply hydrogen atoms so that each carbon atom has four bonds. Step 4 Supply hydrogen atoms so that each carbon atom has four bonds.

Draw structural formulas for the following compounds 2,3-dimethylhexane CH3 CH CH2 1 2 3 4 5 6

3,3-dimethylhexane 2-bromo-3-nitrobutane CH3 CH2 C CH3 CH Br NO2 1 2 3 4 5 6 2-bromo-3-nitrobutane CH3 CH Br 1 2 3 4 NO2

1-bromo-3-nitrobutane CH2 CH CH3 Br 1 2 3 4 NO2

What is the IUPAC name of the following compound? CH3 CH CH2 C2H5 1 2 4 5 6 8 3 7 4-ethyl-2-methyloctane

What is the structure of 2,4-dimethylhexane? 1 2 3 4 5 6 CH3 CH CH2

What is the IUPAC name of the following compound? CH3 CH2 CH 1 2 3 4 5 6 7 4-methylheptane

Cyclo Alkanes

They have the general formula CnH2n Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,… They are named by attaching the prefix cyclo- to the name of the alkane having the same number of carbons as in the ring.

Cycloalkanes are often represented by simple geometrical figures. Cyclopropane is represented by a Cyclobutane is represented by a Cyclopentane is represented by a Cyclohexane is represented by a

It is understood that each corner represents CH2 group. Cyclo Alkanes It is understood that each corner represents CH2 group.

Cyclo Alkanes

Structure of Cyclopropane

Substituted Cycloalkanes are named as The substituent's on the ring are named and their position is indicated by numbers. The ring is numbered so that the substituent's are given the lowest possible Alkylcycloalkanes

The ring is designed as a substituent if the alkane chain contains a greater number of carbon atoms than the ring.

Alkenes

where n = 2,3,… Alkenes have the general formula CnH2n Contain at least one carbon-carbon double bond also called olefins where n = 2,3,…

A Carbon-Carbon Double Bond Consists of a sigma and a pi Bond

CH2 CH CH3 CH3 CH 1-butene 2-butene

cis-dichloroethylene trans-dichloroethylene Cl H C Cl H cis-dichloroethylene trans-dichloroethylene

Rules for Naming Alkene's IUPAC Rules for Naming Alkene's

Rule 1 Select the longest continuous chain of carbon atoms containing the double bond, as the parent chain.

Rule 2 Alkane Alkene -ane +ene Name the longest chain. The name is obtained by replacing ane of alkane with ene. -ane Alkane Alkene +ene Pentene

Number the chain from the end closer to the double bond. Rule 3 Number the chain from the end closer to the double bond.

Rule 4 Indicate the position of the double bond by the number of the first (lowest numbered) carbon atom involved in the double bond. Carbon-2

Rule 5 Alkyl groups and other substituent's are numbered , named and placed as prefixes in alphabetical order.

Alkenes containing two double bonds are named as Rule 6 If more than one double are found then use the prefixes di,tri,tetra,for 2,3 and 4. Alkenes containing two double bonds are named as Alkadienes

Cycloalkenes

In naming Cycloalkenes, number the ring to give the double bonded carbons the numbers 1 and 2 , choose the direction of numbering so that the substituent's get the lowest numbers.

The position of the double bond is not indicated because it is known to be between C-1 and C-2.

Alkynes

Alkynes are hydrocarbons have the general formula CnH2n-2 where Alkynes contain at least one carbon-carbon triple bond

The simplest alkynes is Ethyne commonly called Acetylene

The Bonding in Acetylene

Production of acetylene CH C CH2 CH3 CH3 C 1-butyne 2-butyne CaC2 (s) + 2H2O (l) C2H2 (g) + Ca(OH)2 (aq) Production of acetylene

Rule 1 Select the longest continuous carbon chain containing at least one triple bond, as the parent chain.

Rule 2 alkane Alkynes Hexyne -ane +yne Name the longest chain. The name is obtained by replacing ane of alkane with yne. -ane alkane Alkynes +yne Hexyne

Number the chain from the end closer to the triple bond. Rule 3 Number the chain from the end closer to the triple bond. 1 2 3 4 5 6

Rule 4 Indicate the position of the triple bond by the number of the first (lowest numbered) carbon atom involved in the triple bond. 1 2 3 4 5 6 Carbon -2

Rule 5 Alkyl groups and other substituent's are numbered, named and placed as prefixes in alphabetical order. 1 2 3 4 5 6 5-methyl-2-hexyne

Alkenes containing two triple bonds are named as Rule 6 If more than one triple are found then use the prefixes di,tri,tetra,for 2,3 and 4. Alkenes containing two triple bonds are named as Alkadiyne

Alkyl halides are compounds which contain carbon-halogen bonds. They are classified as primary, secondary,and tertiary alkyl halides. Abbreviations for these terms are 1°, 2°, and 3°, respectively.

The common names of alkyl halides are obtained by naming the alkyl group attached to the halogen and adding the name of the halide as a separate word

Naming Alkyl Halides Alkyl halides are named in the same way as alkanes by treating the halogen as substituent on a parent alkane chain.

Select the longest continuous carbon chain as the parent chain. Rule 1 Select the longest continuous carbon chain as the parent chain.

Number the chain from the end closer to the substituent's. Rule 2 Number the chain from the end closer to the substituent's. 1 2 3 4 5 6

Rule 3 If more than one of the same kind of halogen is present, number each and use one of the prefixes di-, tri-, tetra-, and so on.

Rule 4 If different halogens are present, number each according to its position on the chain and list them in alphabetical order when writing the name.

CH3I can be called methyl iodide. In addition to their systematic names, many simple alkyl halides are also named by identifying first the alkyl group and then the halogen. For example, CH3I can be called methyl iodide. Such names are well entrenched in the chemical literature and in daily usage.

Alcohols Alcohols are compounds in which a hydroxyl group (-OH) is bonded to a saturated carbon.

Classification of alcohals They are classified as primary, secondary, or tertiary alcohal. Abbreviations for theses terms are 1°, 2°, and 3°, respectively.

Primary Acohal

SecondaryAcohal

Tertiary cohal

IUPAC Rules for naming Alcohols.

Rule 1 Select the longest continuous carbon chain to which the hydroxyl group is attached as the parent chain.

The name is obtained by replacing the final -e with-ol. Rule 2 Name the longest chain The name is obtained by replacing the final -e with-ol. -e alkane Alkanol +ol

Rule 3 Number the chain to give the lowest number to carbon attached to the hydroxyl group.

Rule 4 Indicate the position of the hydroxyl group by the number of the carbon attached to the hydroxyl group.

Rule 5 Other substituent's are numbered, named, and placed as prefixes in alphabetic order For example:

Rule 6 Alcohols containing two or three –OH groups are named as Alkanediols and Alkanetriols respectively. Notice that –e of the corresponding alkane name is retained.

IUPAC Rules for Naming Aldehydes Select the longest chain containing the aldehyde group.

Rule 2 Alkane -e + al = Alkanal Pentanal Name the longest chain. The name is obtained by dropping the final .e from the name of the corresponding alkane, and adding the ending -al Alkane -e + al = Alkanal Pentanal

Number the chain by assigning the number 1 to the aldehyde carbon. Rule 3 Number the chain by assigning the number 1 to the aldehyde carbon. 1 5 4 3 2

Rule 4 Other substituent's are numbered, named, and placed as prefixes in alphabetic order.

Notice that .e of the corresponding alkane name is retained. Rule 5 When there are two aldehyde groups in a molecule, it is named as “Alkanedial”. Notice that .e of the corresponding alkane name is retained.

Ketones Ketones are compounds in which carbonyl group (C=O) is bonded to two organic groups.

Select the longest chain containing the carbonyl carbon atom. IUPAC Rules for naming Ketones Rule 1 Select the longest chain containing the carbonyl carbon atom.

Alkane -e + one = Alkanone. Rule 2 Name the longest chain. The name is obtained by dropping the final-e from the name of the corresponding alkane, and adding the ending .one. Alkane -e + one = Alkanone.

Number the chain to give the lowest number to the carbonyl carbon. Rule 3 Number the chain to give the lowest number to the carbonyl carbon. 1 5 4 3 2

Rule 4 Other substituent's are numbered, named, and placed as prefixes in alphabetic order. 1 5 4 3 2

Rule 5 When there are two carbonyl groups in a molecule, it is named as Alkanedione.

Rule 6