CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY FKA 0252 CHEMISTRY IV

OUTLINE 1.INTRODUCTION Organic compounds Bonding of carbon atoms Classification of carbon atoms in organic compounds 2.EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULA 3.FUNCTIONAL GROUPS 4.ISOMERISM Constitutional isomerism Stereoisomerism 5.ORGANIC REACTIONS Types of cleavage, reactants and reactions

INTRODUCTION Organic Chemistry - A subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of carbon-based compounds, hydrocarbons, and their derivatives. - Not all carbon-containing compounds are classified as organic. - Organic compounds: covalently bonded compounds containing carbon, excluding carbonates and oxide s.

Examples INTRODUCTION nicotine methane urea adrenaline aspirin glycerol caffeine

INTRODUCTION cholesterolDDT (insecticide) acetylcholine Linoleic acid penicillin

- Carbon when combines with other elements (N, O, S, halogens) forms different classes of organic compounds. - Saturated organic compounds: C-C single bonds (alkanes, cycloalkanes) - Unsaturated organic compounds: Carbon multiple bonds (alkenes, alkynes) Able to undergo addition reactions. INTRODUCTION

Bonding of Carbon Atoms - Carbon can form 4 covalent bonding with other C atoms or other elements. - Covalent bonds: C-C, C-H, C=O, C=C, C≡C and others. Involve a number of hybrid orbitals such as sp 3, sp 2 and sp. - Hybrid orbital of C atoms depends on the no. of bonding electron pairs and lone electron pairs. - Carbon atoms cannot expand octet, no sp 3 d and sp 3 d 2 hybrids INTRODUCTION

In determining the hybrid orbitals of C atoms, multiple bonds are regarded as single bonds. INTRODUCTION

Types of Bonds INTRODUCTION Single bond, e.g Ethane - Two carbon atoms share a pair of electrons Double bond, e.g Ethene - Two carbon atoms sharing two pairs of electrons Triple bond, e.g Ethyne - Two carbon atoms share three pairs of electrons

Classification of Carbon Atoms in Organic Compounds - Five types of carbon atoms: INTRODUCTION

- Only 3 classes of hydrogen atom: Primary (1 o ), secondary (2 o ) and tertiary (3 o ) NO quarternary H atom. INTRODUCTION 1 o H atom – Hydrogen atom directly bonded to a 1 o carbon atom 3 o H atom – H ydrogen atom directly bonded to a 3 o carbon atom 2 o H atom – Hydrogen atom directly bonded to a 2 o carbon atom

EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULAE Empirical Formula - A chemical formula: gives the simplest ratio of all atoms of each element in a compound. - Empirical formula of glucose, C 6 H 12 O 6 is CH 2 O - MUST consist of integers (not decimal or fraction). Molecular Formula - Chemical formula: shows the exact number of all atoms of each element in a compound. - Example: Vitamin C Empirical Formula: C 3 H 4 O 3 Molecular formula: C 6 H 8 O 6

Structural Formula - A chemical formula shows how the atoms in a molecule are bonded to each other - 3 types : Expanded – Shows how atoms are attached to each other. Single line represented a bond pair Condensed – Does not show the covalent bonds. Brackets and subscript are used for repeating groups Skeletal – Does not show carbon and hydrogen atoms, only show functional groups EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULAE

ExpandedCondensedSkeletal Propene 2-butanol Methylcyclo- butane EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULAE

ExpandedCondensedSkeletal 3-methyl- butanone 2-bromo- butane EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULAE

ExpandedCondensedSkeletal 2-methyl-1- propanamine Ethyl methanoate EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULAE

Three Dimensional Structure Fischer Projection (wedge) – bond that lies out of the plane (dashed wedge) – bond that lies behind the plane (line) – bond that in the plane Vertical line – bonds that project behind the plane Horizontal line – bonds that project out of the plane Intersection of lines represents a C atom EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULAE

FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES Functional group : An atom or a group of atoms which characterizes the molecule and determines its chemical properties. Homologous series : Series of compounds with the same functional group and each member differs from the next member by a CH 2 unit.

Homologous Series Functional GroupExample General Formula AlkaneNoneC n H 2n+2 Alkene (carbon-carbon double bond) C n H 2n Alkyne (carbon-carbon triple bond) C n H 2n-2 FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES

Homologous Series Functional GroupExample General Formula Arene Benzene ring- Haloalkane X = halogen (F/Cl/Br/I) C n H 2n+1 X Alcohol (Hydroxyl) C n H 2n+1 OH FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES

Homologous Series Functional GroupExample General Formula Ether (alkoxy) C n H 2n+2 O Aldehyde (carbonyl) C n H 2n O Ketone (carbonyl) C n H 2n O Nitrile (cyano) C n H 2n+1 CN FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES

Homologous Series Functional GroupExample General Formula Carboxylic Acid (carboxyl) C n H 2n O 2 Ester (carboalkoxy) C n H 2n O 2 Acyl Chloride (acyl) - Amide (carboxamide) - FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES

Homologous Series Functional GroupExample General Formula Amine (amino) C n H 2n+1 NH 2 Acid anhydride (acid anhydride) - FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES

Isomerism Constitutional Isomerism ChainPositionalFunctional Group StereoisomerismCis-trans isomerismOptical isomerism Compounds which have the same molecular formula but different structural formula ISOMERISM

Constitutional Isomerism Chain isomers – differ in the number of longest carbon (also in physical properties). Example: pentane and 2- methylbutane Positional isomers – differ at the position (no. of C atom) at which the functional group is bonded to. - Have different physical properties but have similar chemical properties. ISOMERISM

Functional group isomers – isomers with same general molecular formula but are from different class. - Have different physical and chemical properties. ISOMERISM C3H8OC3H8O AlcoholEther C 5 H 10 O KetoneAldehyde

Strategies in writing all the possible isomers of C 7 H 16 : ISOMERISM Draw isomer with longest unbranched open chain Shortened the chain and make a methyl side chain Shift the methyl side chain, a new compound is formed Shortened the carbon chain and make another methyl side chain

Shift both methyl groups to form another isomer Shorten the carbon chain (If possible) Make an ethyl branch ISOMERISM

Stereoisomerism : Compounds which have the same molecular and structural formula but differ in the arrangement of atoms in space. Cis-trans isomerism : arises due to restricted rotation of carbon- carbon double bond and carbon-carbon single bond in cyclic compounds. - There are different atoms or groups of atoms at the same C=C or C-C bond in cyclic compounds. ISOMERISM Is the same molecule as

No cis-trans isomerism  same H atoms at the same C=C bond. Cis-trans due to different atoms/ group of atoms at the same C+C bond. Cis-2-pentenetrans-2-pentene ISOMERISM

cis-trans normally have the same chemical properties (due to the same functional group) but different physical properties. ISOMERISM cis-1,2-dichloroethene polar – higher b.p trans-1,2-dichloroethene Non-polar – lower b.p

Optical Isomerism: isomers which are optically active, able to rotate plane polarized light in a polarimeter and exist as mirror images (enantiomers). ISOMERISM Optically active – molecules MUST have at least one chirality center (asymmetric carbon). Chirality center: sp 3 hybridized atom which bonded to 4 different atoms or groups of atoms. Enantiomers (mirror images) – NOT superimposable on each other like left and right hands.

Examples (optically active compounds): ISOMERISM (Chirality center is labeled *) A B CD E

-The maximum number of stereoisomers  2 n ; n = no. of chirality center.  e.g, For example: -Enantiomers  have same physical and chemical properties.  usually drawn using 3-D structure or Fischer projection formula. ISOMERISM DB 2 1 = 2 stereoisomers2 4 = 16 stereoisomers

For example: (Lactic acid) ISOMERISM (+)(-)

ISOMERISM (+) isomer - dextrorotatory  rotates plane polarized light clockwise (-) isomer - levorotatory  rotates plane polarized light anticlockwise

ORGANIC REACTIONS Types of Cleavage Homolytic cleavage : breaking of covalent bond between the same atoms or different atoms with small electronegativity difference to form free radicals. An endothermic process – energy is absorbed to break the covalent bonds. Energy is provided by sunlight (uv light) or high temperature.

ORGANIC REACTIONS Stability of free radical:

Heterolytic cleavage Involves 2 atoms of different electronegativity Breaking of polar covalent bond whereby both of the bonding electron pair goes to the more electronegative atom (between different atoms)  forming nucleophiles (anions) and electrophiles (cations) ORGANIC REACTIONS

Stability of carbocation (C atoms with positive charge): The inductive effect of alkyl groups or electron donating groups increases from methyl to tertiary carbocations  causes cation less positive or stabilizes the carbocation ORGANIC REACTIONS

Types of Reactants Free radicals: molecules/ atoms which contain unpaired electron  neutral and reactive formed as a result of homolytic cleavage in a covalent bond Example: Electrophiles: molecule/ ion which is electron deficient (low electron density) and attack electron rich species (high electron density) ORGANIC REACTIONS H ●, CH 3 ● and ● Cl Examples: Lewis acids, e- pair acceptors, cations, carbocation, oxidizing agents and lack of octet species

Nucleophiles : molecules/ ions which are electron rich, and have high electron density (possess lone electron pairs and compounds which have π bonds) and attack electron deficient center. ORGANIC REACTIONS Examples: Ammonia, Lewis base, carbanions and species with lone electron pairs Cl - being nucleophile or Lewis base reacts with carbonyl carbon atom which is electron deficient. Electrophile (Lewis acid) Nucleophile (Lewis base)

Stability of carbocation (C atoms with negative charge): ORGANIC REACTIONS The inductive effect of alkyl groups  destabilizes the carbanions.

ORGANIC REACTIONS SubstitutionAddition EliminationRearrangement Types of Reactions

Substitution : involves substituting one atom or group of atoms in a molecule by another atom or group of atoms. - 3 types : ORGANIC REACTIONS Nucleophile substitution Free radical substitution Electrophilic substitution

Addition : involves multiple bonds like C=C and C≡C. - 2 types: ORGANIC REACTIONS Electrophilic addition Nucleophilic addition

Elimination : involves removal of a small molecule from an organic compound which usually results in the formation of double or triple bonds. ORGANIC REACTIONS Water is removed from ethanol to form ethene Water is removed from ethanoic acid to form ester

Rearrangement : involves transfer of one atom, ion or group of atoms within the same molecule. ORGANIC REACTIONS Methyl group shifts together with its bonding electron pair to form a tertiary carbocation which is more stable.