SUMMARY

ORGANIC CHEMISTRY-INTRODUCTORY TOPICSSummary

www.wewwchemistry.com

Carbon forms a huge number of compounds.The study of the structures, reactions and properties of these carbon-based compounds is called organic chemistry.Note:Carbon monoxide, carbon dioxide, metal carbonates and metal cyanides are not classified as organic compounds. What is Organic Chemistry?2www.wewwchemistry.com

www.wewwchemistry.com3Why does carbon form so many compounds? Bonding Natureof CarbonTetravalentCarbon forms four bonds.Due to strong CC bond, it can bond with itself to form stable straight or branched chains, or ring structures.Strong CC bondsCC bonds are much stronger than bonds between atoms of other elements.BondBond energy/ kJ mol1CC350SiSi222NN160OO150

Multiple bondsCarbon can also form single, double or triple bonds with itself.Carbon compounds can have varying degree of unsaturation.

www.wewwchemistry.com4Classification According to Carbon SkeletonOrganic CompoundsAliphaticOpen-chainAlicyclic(closed ring)Straight-chainSaturatedUnsaturatedAromaticContains one or more benzene rings

Branched chain

www.wewwchemistry.com5Homologous SeriesOrganic compounds in the same homologous series:Example: alkenepossess the same general formulaCnH2ndiffer from the previous member in the series by a CH2 groupCH2=CH2, CH2=CHCH2H,CH2=CHCH2CH3, CH2=CHCH2CH2CH3possess similar chemical properties, due to the presence of same functional groupAlkenes possess a carbon-carbon double bond.Alkenes undergo electrophilic addition reactions.show gradual change in physical properties due to increased molecular size and mass, caused by longer carbon chainsEthene b.p. = 102 CPropene b.p. = 48 C1-Butene b.p. = 6.5 C1-Pentene b.p. = 30 C

A functional group is an atom or a group of atoms that governs the chemical properties of an organic molecule.www.wewwchemistry.com6Functional Groups

www.wewwchemistry.com8Functional GroupsClass of compoundFunctional groupName of functional groupHydroxy compoundsRCH2OHPrimary alcoholRR1CHOHSecondary alcoholRR1R2COHTertiary alcoholC6H5OHPhenolCarbonyl compoundsRCHOAldehydeRR1COKetone

where R, R1, R2 represent alkyl groups, CnH2n+1

www.wewwchemistry.com9Functional GroupsClass of compoundFunctional groupName of functional groupCarboxylic acidsRCO2HCarboxylic acidCarboxylic acid derivativesRCOClAcyl chlorideRCO2R1EsterRCONH2AmideAminesRNH2Primary amineRR1NHSecondary amineRR1R2NTertiary amineNitrilesRCNNitrile

where R, R1, R2 represent alkyl groups, CnH2n+1

The structural formulae of organic compounds may be represented usingdisplayed formulaecondensed structural formulaeskeletal formulaeNote that any structural formula given must give an unambiguous structure.E.g. 1-propanolwww.wewwchemistry.com10Writing Structural FormulaeCH3CH2CH2OHC3H7OH

Displayed FormulaeShow both the relative placing of atoms and the number of bonds between them.All bonds between atoms must be shown.Exception:The following convention for representing the aromatic ring is preferred:

www.wewwchemistry.com11Writing Structural Formulae

Condensed Structural FormulaeEach carbon atom is written separately.Following each of these carbon atoms,the other atoms that are bonded to this carbon atom are written.Substituent groups that are bonded to this carbon atom are enclosed in brackets.Similarly, the following convention for representing the aromatic ring is preferred: www.wewwchemistry.com12Writing Structural Formulae

Skeletal FormulaeSimplified representation derived from a structural formula by removing hydrogen atoms (and their associated bonds) and carbon atoms from alkyl chains, leaving just the carbon-carbon bonds in the carbon skeleton and the associated functional groups.The following convention for representing the aromatic ring is preferred:www.wewwchemistry.com13Writing Structural Formulae

IUPAC Nomenclature is a system of naming chemical substances developed by the International Union of Pure and Applied Chemistry (IUPAC).The IUPAC sets global standards for names, symbols, and units used in chemical sciences.www.wewwchemistry.com16IUPAC Nomenclature

The IUPAC name for an organic compound consists of the following parts:www.wewwchemistry.com17IUPAC NomenclatureRootSuffix(es)InfixPrefix(es)No. of carbon atoms in longest continuous carbon chain, i.e. parent chainNature of parent chainSide chains & functional groups of lower priority1 suffix2 suffixDegree of saturation or unsaturationFunctional group of highest priority in molecule+

www.wewwchemistry.com18IUPAC Nomenclatureroot(no. of carbon atomsin parent chain)1 suffix(degree ofsaturation)2 suffix(main functional group,of highest priority)side-chains &functional groups of lower priority, arranged in alphabetical orderinfix(nature ofparent chain)

3-ethyl-4-methylhexane

3-oxohexanal

2-hydroxypropanoic acid3-methylcyclopentene

123Locants indicate positions of sustituent groups, bonds etc. in molecule

locantlocantlocant

www.wewwchemistry.com19IUPAC Nomenclature

(Source: http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry)18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-diene-19-yne-3,9-dione

root(no. of carbon atomsin parent chain)1 suffix(degree ofsaturation)2 suffix(main functional group,of highest priority)side-chains &functional groups of lower priority,arranged in alphabetical orderLocants indicate positions of sustituent groups, bonds etc. in molecule

tricos 23 carbons

Punctuation rules:Di-, tri- etc. are not taken into consideration when arranging side-chains and functional groups alphabetically.Commas are placed between numbers.Hyphens are placed between a number and a letter.All parts are connected either by merging successive names, including commas or hypens to form a one-word name.www.wewwchemistry.com20IUPAC Nomenclature

Functional groups control the chemistry of organic molecules.They contain reactive sites:Electron deficient sitesE.g. a carbon atom bonded to a more electronegative bromine atomElectron rich sitesE.g. a -system in an alkene or a benzene ringwww.wewwchemistry.com21Organic Reactions

www.wewwchemistry.com23Organic ReactionsTypes ofBond FissionHomolyticWhen a covalent bond between two atoms breaks, each atom retains one bonding electron.Free radicals are formed.A free radical is an electrically neutral atom or group of atoms that has one unpaired electron. It is unstable and highly reactive.ClCl Cl + ClHeterolyticWhen a covalent bond between two atoms breaks, one of the atoms retains both the bonding electrons to bear a negative charge.The other atom bears a positive charge.HCl H+ + Cl:

www.wewwchemistry.com24Organic ReactionsTypes ofReagentsNucleophileA reagent that is attracted to regions of positive charge or electron deficient sitesAn electron pair donorGood bases are generally good nucleophilesNegative ions: HO:, NC:Neutral molecules: H2O:, :NH3 A reagent that is attracted to regions of negative charge or high electron densityAn electron pair acceptorElectrophilePositive ions: NO2++ end of an induced dipole: +BrBr+ end of a permanent dipole: +HCl

Isomers are molecules that have the same molecular formula but different arrangement of atoms in space.www.wewwchemistry.com25IsomerismIsomerismStructural isomerismSame molecular formulaDifferent structural formulaeStereoisomerismSame molecular formulaSame structural formulaDifferent spatial arrangement of atoms in 3D spaceChainisomerismFunctionalisomerismPositionalisomerismCis-transisomerismOpticalisomerism

Chain IsomerismArises due to the different arrangement of carbon atoms in a carbon chain.E.g. isomers of hexane, C6H14www.wewwchemistry.com26Structural Isomerism

Positional IsomerismArises due to the different positions assumed by a functional group on a carbon chain or ring.www.wewwchemistry.com27Structural Isomerism

pentan-1-olpentan-2-olpentan-3-ol

2-chloromethylbenzene3-chloromethylbenzene4-chloromethylbenzene

Cis-trans (a.k.a. geometric) isomerism[Use of E-Z nomenclature is not required by the 9647 syllabus.]Criteria:Restricted rotation about a double bond, e.g. carbon-carbon double bond, orRestricted rotation due to a rigid ring structureTwo different substituent groups attached to each atom in a double bond, e.g. to each carbon atom in a carbon-carbon double bondwww.wewwchemistry.com29Stereoisomerism

Optical isomerismCriteria: A chiral carbon, i.e. an asymmetrical carbon atom with four different substituent groupsNo plane of symmetryOptical isomers exist as a pair of nonsuperimposable mirror images of each other.Optical isomers are also known as enantiomers.www.wewwchemistry.com32Stereoisomerism

Enantiomers Identical chemical properties and physical propertiesRotate plane of polarised light in opposite directionswww.wewwchemistry.com33Stereoisomerism

Racemic mixtureEqual amounts of both enantiomers.Optically inactive, as there is no net rotation of plane-polarised light. Although both enantiomers rotate plane-polarised light in opposite directions, the rotations cancel out. www.wewwchemistry.com34Stereoisomerism

Drawing optical isomersOptical isomers must be drawn as three-dimensional structures according to the convention used in the example below:www.wewwchemistry.com35Stereoisomerism

(Source: Higher 2 Chemistry Syllabus 2013/9647)