ObjectivesAfter this chapter, you will:• Learn and differentiate functional groups• Learn to name organic compounds according to IUPAC nomenclature and draw correct structure• Learn about types of isomerism
Introduction to Organic Chemistry• Organic compounds are classified into different types, such as alkanes, alkenes, alcohols, amines and etc.• Each type of organic compound contains the same reactive group of atoms, which is called functional group. E.g. alcohols contain the –OH functional group
Functional GroupsFunctional Group StructureAlkane R–HAlkene (Olefin) C=C (ethylenic bond)Alkyne C≡C (acetylenic bond)Alcohol R – O – H (hydroxyl)Arenes (aromatic Ar (Aryl)hydrocarbon)Aldehyde O R–C–H
Functional Group StructureKetone O R – C – R’Carboxylic Acid O (carboxyl) R – C – OHEster O R – C – O – R’
Functional Group StructureAnhydride O O R – C – O – C – R’Amide O R – C – NH2Amine R – NH2Nitrile
IUPAC Nomenclature• IUPAC International Union of Pure & Applied Chemistry• The IUPAC nomenclature system is a set of logical rules devised and used by organic chemists to name the organic compounds.
IUPAC Rules1. Select the longest continuous C chain as parent chain (use root word for the no. of C)2. Name each of the branch/substituents as an alkyl / aryl group3. Number the C chain begin from the end nearest to the branch ⇒ branch/substituents appear at the lowest no. possible
4. Name each substituent according to its chemical identity & the no. of the C atom to which it is attached ⇒ For identical substituent, use the prefix di, tri… & write appropriate C no. for each substituent5. Separate no. from no. by commas (,) & no. from letters by hyphens (-)6. List the substituents alphabetically by name ⇒ di, tri…. don’t count
IUPAC Nomenclature Functional Group NomenclatureAlkane End with -aneAlkene End with –eneArene End with –benzeneAlcohol End with –olAldehyde End with –alKetone End with –one
Functional Group NomenclatureCarboxylic acid End with –oic acidEster End with –oatAnhydride End with –oic anhydrideAmine End with –amineAmide End with –amideNitrile End with –nitrile
Base NamesPrefix No. of Prefix No. of Carbons (n) Carbons (n)Meth 1 Hex 6Eth 2 Hept 7Prop 3 Oct 8But 4 Non 9Pent 5 Dec 10
Straight-Chain Alkyl Groups, R Alkyl group Name (abbreviation) −CH3 Methyl (Me) −CH2CH3 Ethyl (Et) −CH2CH2CH3 Propyl (Pr) −CH2CH2CH2CH3 Butyl (Bu) −CH2CH2CH2CH2CH3 Pentyl• Alkyl groups are named by replacing the –ane ending of the parent alkane with an –yl ending
Naming of Identical Branch SubstituentsNo. of substituents Prefix 2 Di 3 Tri 4 Tetra
IsomerismDefinition of isomerism:• A phenomena where 2 or more compounds have the same molecular formulae but with different arrangements of their constituent atoms• Such molecules are known as isomers
Isomerism Isomerism Structural StereoisomerismIsomerism Optical Isomerism Chain Isomerism Geometric Position Isomerism Isomerism Functional Group Isomerism
Structural Isomerism• Isomers have the same molecular formulae but different structural formulae 1. Chain Isomerism• The isomers are from the same homologous series & have the same functional groups but different type of carbon chain.• Example: C4H10
2. Position Isomerism• The isomers are from the same homologous series & have the same functional groups but the position / location of the functional group is different• Same C skeleton• Example: C3H8O
3. Functional Group Isomerism• The isomers are from different homologous series & have different functional groups• The chemical & physical properties are different• Example: C3H6O
Geometric Isomerism (Cis-trans Isomerism)• The atoms making up the isomers are joined up in the same order, but manage to have a different spatial arrangement.• Due to restricted rotation of groups in double bonds & in cyclic compounds.
Example: Geometric Isomerism H Cl H H C C C C Cl H Cl Cltrans-1,2-dichloroethene cis-1,2-dichloroethene• trans isomer − 2 chlorine atoms are locked on opposite sides of the double bond (trans : Latin meaning "across“)• cis isomer − 2 chlorine atoms are locked on the same side of the double bond (cis : Latin meaning "on this side")
The Effect of Geometric Isomerism on Physical Properties1. cis isomer has higher boiling point.• Bp depends on the polarity of the molecules• cis isomers are > polar, stronger attractive intermolecular forces exist between cis isomer2. trans isomer has higher melting point.• Mp depends on the arrangement & packing of molecules in the crystal lattice• trans isomer with > symmetrical structure, can be > closely packed in the crystal lattice
?? Cis-isomer has higher bp• e.g. 1,2-dichloroethene• 1 side will be more positive charge & the other side more negative ⇒ polar• Van der Waals + dipole-dipole interaction• Need extra energy ⇒ bp increases
?? Trans-isomer has lower bp• the slight charge on the top of the molecule is exactly balanced by an equivalent charge on the bottom• No dipole-dipole force as it is non-polar molecule.• Thus, only held by weak Van der Waals• Less energy needed ⇒ lower bp
?? Trans-isomer has lower bp• Trans-isomer• No dipole-dipole force as it is non-polar molecule.• Thus, only held by weak Van der Waals• Less energy needed ⇒ lower bp
?? Trans-isomer has higher mp• trans isomer has the higher melting point Melting point = solid ⇒ solution• In order for the intermolecular forces to work well, the molecules must be able to pack together efficiently in the solid.• Trans isomers pack better than cis isomers. The "U" shape of the cis isomer doesnt pack as well as the straighter shape of the trans isomer.
?? Cis-isomer has lower mp• The poorer packing in the cis isomers means that the intermolecular forces arent as effective be• Less energy is needed ⇒ mp lower
Optical Isomerism• Optical isomers are 2 compounds with the same structural formulae, but one isomer is the mirror image of the other & cannot be superimposed on one another in any orientation• It occurs when 4 different groups of atoms are joined to a C atom by 4 single covalent bonds.
Optical Isomerism• Occurs because of the tetrahedral bonding around a C atom• Structures that can exist as 2 optical isomers are said to be optically active & possess a chiral centre• Simple substances which show optical isomerism exist as two isomers known as enantiomers• Chiral centre = atom bond with the 4 different groups, which is normally marked with an asterisk (∗)