chapter 1 introduction to organic chemistry

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  • 1.FHSC1124Organic ChemistryIntroduction to OrganicChemistry Chapter 1

2. Chapter Scopes Introduction Homologous series Functional groups Naming/Nomenclature Isomerisms 3. ObjectivesAfter this chapter, you will: Learn and differentiate functionalgroups Learn to name organic compoundsaccording to IUPAC nomenclatureand draw correct structure Learn about types of isomerism 4. Introduction to Organic Chemistry 5. Introduction to Organic Chemistry Organic compounds are classified intodifferent types, such as alkanes, alkenes,alcohols, amines and etc. Each type of organic compound containsthe same reactive group of atoms, which iscalled functional group. E.g. alcohols contain the OH functionalgroup 6. Functional GroupsFunctional Group StructureAlkane RHAlkene (Olefin) C=C (ethylenic bond)Alkyne CC (acetylenic bond)AlcoholR O H (hydroxyl)Arenes (aromaticAr (Aryl)hydrocarbon)AldehydeO RCH 7. Functional GroupStructureKetone O R C RCarboxylic AcidO(carboxyl) R C OHEster O R C O R 8. Functional GroupStructureAnhydrideO O R C O C RAmide O R C NH2Amine R NH2Nitrile 9. IUPAC Nomenclature IUPAC International Union of Pure &Applied Chemistry The IUPAC nomenclature system is a setof logical rules devised and used byorganic chemists to name the organiccompounds. 10. 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 lowestno. possible 11. 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. dont count 12. IUPAC Nomenclature Functional GroupNomenclatureAlkaneEnd with -aneAlkeneEnd with eneArene End with benzeneAlcohol End with olAldehydeEnd with alKetoneEnd with one 13. Functional GroupNomenclatureCarboxylic acid End with oic acidEster End with oatAnhydride End with oic anhydrideAmine End with amineAmide End with amideNitrile End with nitrile 14. Base NamesPrefix No. ofPrefix No. of Carbons (n)Carbons (n)Meth 1 Hex 6Eth2 Hept7Prop 3 Oct 8But4 Non 9Pent 5 Dec10 15. Straight-Chain Alkyl Groups, R Alkyl group Name (abbreviation)CH3Methyl (Me)CH2CH3 Ethyl (Et)CH2CH2CH3Propyl (Pr)CH2CH2CH2CH3 Butyl (Bu) CH2CH2CH2CH2CH3Pentyl Alkyl groups are named by replacing theane ending of the parent alkane with anyl ending 16. Naming of IdenticalBranch SubstituentsNo. of substituents Prefix 2 Di 3 Tri 4Tetra 17. IsomerismDefinition of isomerism: A phenomena where 2 or morecompounds have the same molecularformulae but with different arrangementsof their constituent atoms Such molecules are known as isomers 18. IsomerismIsomerism StructuralStereoisomerismIsomerismOpticalIsomerism Chain IsomerismGeometric Position Isomerism Isomerism Functional Group Isomerism 19. Structural Isomerism Isomers have the same molecular formulaebut different structural formulae 1. Chain Isomerism The isomers are from the same homologousseries & have the same functional groups butdifferent type of carbon chain. Example: C4H10 20. 2. Position Isomerism The isomers are from the samehomologous series & have the samefunctional groups but the position / locationof the functional group is different Same C skeleton Example: C3H8O 21. 3. Functional Group Isomerism The isomers are from different homologousseries & have different functional groups The chemical & physical properties aredifferent Example: C3H6O 22. Geometric Isomerism(Cis-trans Isomerism) The atoms making up the isomers arejoined up in the same order, but manage tohave a different spatial arrangement. Due to restricted rotation of groups indouble bonds & in cyclic compounds. 23. Example: Geometric IsomerismH Cl HHC CC C Cl H ClCltrans-1,2-dichloroethene cis-1,2-dichloroethene trans isomer 2 chlorine atoms are lockedon opposite sides of the double bond(trans : Latin meaning "across) cis isomer 2 chlorine atoms are lockedon the same side of the double bond(cis : Latin meaning "on this side") 24. The Effect of Geometric Isomerismon 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 25. ?? Cis-isomer has higher bp e.g. 1,2-dichloroethene 1 side will be more positive charge & theother side more negative polar Van der Waals + dipole-dipole interaction Need extra energy bp increases 26. ?? Trans-isomer has lower bp the slight charge on the top of the moleculeis exactly balanced by an equivalentcharge on the bottom No dipole-dipole force as it is non-polarmolecule. Thus, only held by weak Van der Waals Less energy needed lower bp 27. ?? Trans-isomer has lower bp Trans-isomer No dipole-dipole force as it is non-polarmolecule. Thus, only held by weak Van der Waals Less energy needed lower bp 28. ?? Trans-isomer has higher mp trans isomer has the higher melting point Melting point = solid solution In order for the intermolecular forces towork well, the molecules must be able topack together efficiently in the solid. Trans isomers pack better than cisisomers. The "U" shape of the cis isomerdoesnt pack as well as the straightershape of the trans isomer. 29. ?? Cis-isomer has lower mp The poorer packing in the cis isomersmeans that the intermolecular forces arentas effective be Less energy is needed mp lower 30. Optical Isomerism Optical isomers are 2 compounds with thesame structural formulae, but one isomeris the mirror image of the other & cannotbe superimposed on one another in anyorientation It occurs when 4 different groups of atomsare joined to a C atom by 4 single covalentbonds. 31. Optical Isomerism Occurs because of the tetrahedral bondingaround a C atom Structures that can exist as 2 opticalisomers are said to be optically active &possess a chiral centre Simple substances which show opticalisomerism exist as two isomers known asenantiomers Chiral centre = atom bond with the 4different groups, which is normally markedwith an asterisk () 32. Example: Optical IsomerismChiralcentre 33. Example: Optical Isomerism It is important thistime to draw theCOOH groupbackwards in themirror image.Incorrect 34. ExerciseFor each of the following molecules, draw thepossible stereoisomers and state the type ofstereoisomers shown.(a) C6H5CH=CHCOOH(b) C6H5CH(Cl)CH=CH2(c) CH3CH=CHCH3(d) CH3CH2CH(NH2)COOH 35. Summary use IUPAC nomenclature to name anddraw correct structure of simple organiccompounds with different functionalgroups. Differentiate types of isomerism and drawisomers.