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TAMPINES JUNIOR COLLEGE 2014 JC1 Chemistry H2 Level - Introduction to Organic Chemistry Lecture Outline: 1. 2 Introduction 1.1 Formulae of Organic Compounds 1.2 Functional Groups 1.3 Homologous Series 1.4 Systematic Naming of Organic Compounds 1.5 IUPAC Rules 1.6 Hybridisation of Carbon Atom 1.7 Concept of Sigma () Bond and Pi () Bond 1.8 Shapes and Bond Angles of Organic Molecules Isomers 2.1 Isomerism 2.2 Formula for Determining the Number of Stereoisomers 2.3 Biological Properties of Stereoisomers References: 1) Chemistry in Context by Hill & Holman 2) Understanding Advanced Organic and Analytical Chemistry by Chan & Tan 3) Principle Of Organic Chemistry/2nd Edition /Pg 14-23 by Peter R.S. Murray TPJC/H2 Chem/Intro Organic Chem Part 1/ 1 Learning Objectives (9647 Syllabus) At the end of this series of lectures, you should be able to: (a) interpret, and use the nomenclature, empirical, molecular, structural, skeletal and displayed formulae of the following classes of compound: (i) alkanes, alkenes and arenes (ii) halogenoalkanes and halogenoarenes (iii) alcohols (including primary, secondary and tertiary) and phenols (iv) aldehydes and ketones (v) carboxylic acids, acyl chlorides and esters (vi) amines, amides, amino acids and nitriles (b) interpret, and use the following terminology associated with organic reactions: (i) functional group (ii) homolytic and heterolytic fission Will be (iii) free radical, initiation, propagation, termination covered in the other (iv) nucleophile, electrophile sub-topics (v) addition, substitution, elimination, hydrolysis (vi) oxidation and reduction [in equations for organic redox reactions, the symbols [O] and [H] are acceptable] (c) describe sp3 hybridisation, as in ethane molecule, sp2 hybridisation, as in ethene and benzene molecules, and sp hybridisation, as in ethyne molecule (d) explain the shapes of, and bond angles in, the ethane, ethene, benzene, and ethyne molecules in relation to σ and π carbon-carbon bonds (e) predict the shapes of, and bond angles in, molecules analogous to those in (d) (f) describe structural isomerism (g) describe geometrical isomerism in alkenes, and explain its origin in terms of restricted rotation due to the presence of π bonds [use of E, Z nomenclature is not required] (h) explain what is meant by a chiral centre (i) deduce whether a given molecule is optically active based on the presence or absence of chiral centres and/or a plane of symmetry (j) recognize that optical isomers have identical physical properties except in the direction in which they rotate plane-polarised light (k) recognize that optical isomers have identical chemical properties except in their interactions with another chiral molecule (l) recognize that different stereoisomers exhibit different biological properties, for example in drug action (m) deduce the possible isomers for an organic molecule of known molecular formula (n) identify chiral centres and/or geometrical isomerism in a molecule of given structural formula TPJC/H2 Chem/Intro Organic Chem Part 1/ 2 Part 1: Introduction 1.0 Introduction What is Organic Chemistry ? Organic chemistry is the chemistry of __________ compounds The word ‘Organic’ , originally used to relate carbon compounds which were obtained from living organisms; Organic Compounds : urea ( H2N-C-NH2 ), starch (C6H10O5)n ll proteins, fatty acids ..... O 1.1 Non-organic / Inorganic compounds : CO32 , SCN , CN , CO .... Formulae of Organic Compounds Objective: Candidates should be able to: (a) interpret, and use the nomenclature, empirical, molecular, structural, skeletal and displayed formulae of the following classes of compound: alkanes, alkenes and arenes, halogenoalkanes and halogenoarenes, alcohols (including primary, secondary and tertiary) and phenols, aldehydes and ketones, carboxylic acids, acyl chlorides and esters, amines, amides, amino acids and nitriles In candidates’ answers, an acceptable response to a request for a structural formula will be to give the minimal detail, using conventional groups, for an unambiguous structure, e.g. CH 3CH2CH2OH for propan-1ol, not C3H7OH. i. Empirical formula: Formula which shows the whole number ratio of atoms of different elements in the compound. e.g. glucose, ( CH2O ) ii. Molecular formula: Formula which shows the number of atoms of each elements present in the compound. e.g. glucose, ( C 6H12O6 ) iii. Structural formula: Formula which shows e.g. ethanol, CH3CH2OH iv. atoms in the molecule are joined together. Displayed formula: Formula which shows both the relative placing / ______________ of atoms and the number of bonds between them e.g. ethane , C2H6 H covalent bonds in the molecule must be shown. It’s a 2-D Flat diagrams in which the bond angles are not what they seem, HCH =109.5 O not 90 O . Two exceptions of acceptable displayed formulae are: H H C C H H and benzene or aromatic ring cyclohexane ring TPJC/H2 Chem/Intro Organic Chem Part 1/ 3 H v. Stetreo-chemical formula (3-D) : C Structural formula which indicates the orientation of the atoms in space and the shape of the molecule 109.5 O 3-D Wedge diagrams Indicates bonds _____________ the plane of the paper Indicates bonds ______________________the plane of the paper Indicates bonds ________________the plane of the paper vi. Skeletal formula: represents pentane ( a 5-C alkane) represents butanol ( a 4-C alcohol) OH 1.2 Functional Group Objective: Candidates should be able to: (b) interpret, and use the following terminology associated with organic reactions: functional group Functional group refers to the part / portion of the organic molecule that is chemically reactive or more reactive which governs the principal chemical properties of the series or class of organic compounds. e.g CH3─CH2 ─OH Alkanes and benzene molecules contain no specific portion of the molecule that is more reactive. Every part of the molecule is similar in reactivity. H methane , CH4 C H H H H benzene H H ≡ H Note that all C- H bonds are identical! H H TPJC/H2 Chem/Intro Organic Chem Part 1/ 4 1.3 Homologous Series ( H. S.) Homologous series refers to a series of compounds in which each member differs from the next by a constant amount of ______units (-CH2-). Each member is called a homolog. Homologous Series of Alkane Family ( C1 C10 ) Table-1.1 : Molecular formula CH4 C2 H6 C3 H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 IUPAC Prefix methethpropbutpenthexheptoctnondec- IUPAC name methane ethane propane butane pentane hexane heptane octane nonane decane nth member nth member CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 CH3CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH2CH3 CH3CH2CH3CH2CH2CH2CH2CH2 CH3CH2CH2CH2CH2CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 General formula: CnH2n+2 Table-1.2 Molecular formula CH3-OH C2H5-OH C3H7-OH C4H9-OH C5H11-OH C6H13-OH C7H15-OH C8H17-OH C9H19-OH C10H21-OH Structural formula The Homologous Series of Alcohols ( C 1 C10 ) IUPAC Prefix methethpropbutpenthexheptoctnondec- IUPAC name methanol ethanol propanol butanol pentanol hexanol heptanol octanol nonanol decanol Structural formula CH3-OH CH3CH2-OH CH3CH2CH2-OH CH3CH2CH2CH2-OH CH3CH2CH2CH2CH2-OH CH3CH2CH2CH2CH2CH2-OH CH3CH2CH2CH2CH2CH2CH2-OH CH3CH2CH2CH2CH2CH2CH2CH2-OH CH3CH2CH2CH2CH2CH2CH2CH2CH2-OH CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2-OH General formula: CnH2n+2O (or CnH2n+1OH ) TPJC/H2 Chem/Intro Organic Chem Part 1/ 5 Table-1.3 Some Common Functional Groups (A-level Course) (Refer to Annex 1 for more details Pg 24-25) 1.3.1 Special Features of Some important functional Groups A. Hydrocarbon C H 1. e.g H Alkane C with C All C-H bonds are similar. Non-reactive C. H H 2. 3. * H C e.g single bonds , tetrahedral shape; H C H Alkene C , with single + double bonds, trigonal planar shape; Very reactive C. H Bezene C , with 2 single +1 double bonds, e.g trigonal planar shape; unreactive benzene ring. Benzene ring showing delocalized -bonds * = actual structure of benzene ring with delocalized -bond (This structure should be drawn in the A level syllabus) B. 4. Hydroxy Compounds e.g C Alcohol C with shape; OH single bonds , tetrahedral O-H is the reactive functional group. 5. * e.g OH Phenolic C , with 2 single +1 double bonds, trigonal planar shape. Both -OH and benzene ring are reactive. Phenol with benzene ring showing delocalized -bonds * OH = actual structure of phenol with benzene ring with delocalised -bond (This structure should be drawn in the A level syllabus) TPJC/H2 Chem/Intro Organic Chem Part 1/ 6 C. 6. Compounds with Carbonyl group R ` e.g C O Aldehyde H ` 7. R’ ` e.g C R ` HO `X e.g 1.4 C O C Ketone O O H ` R’ O R ` 8. C C O R ` Carboxylic acid C O HO `X Systematic Naming (Nomenclature) Of Alkanes & Other Organic Compounds IUPAC = International Union of Pure & Applied Chemistry Used for compounds even with complicated structures. Systematic naming of organic compounds generally have these components: prefix parent stem suffix prefix indicates the number, name and position of the substituents parent stem specifies the number of C-atom in the longest C-chain. suffix indicates the homologous series (functional group) the molecule belongs to (refer to Table 1.3 in the Annex for nomenclature). e.g 1 2 3 4 5 6 CH3CHCH2CH2CH2 CH3 CH3 Prefix parent stem 2-methyl suffix -ane -ene -one hex Suffix ane homologous series alkanes alkenes ketones TPJC/H2 Chem/Intro Organic Chem Part 1/ 7 1.5 IUPAC Rules (Systematic Nomenclature): To name a compound with branched or otherwise substituted chain, these steps are followed: a) Identify the longest chain of carbon atoms & assign the parent name of the compound from the number of carbons. CH3CHCH2CHCH2 CH2CH3 e.g. 1 CH2CH3 CH3 longest C-chain = parent name is ______________ e.g. 2 CH3CHCH2CHCH2CH3 CH2 CH2CH3 CH3 longest C-chain = parent name is ______________ b) Number the parent chain beginning at the end which will result in the lowest possible numbers for the substituents attached to the chain. 7 6 5 4 3 2 1 1 2 3 4 5 6 7 CH3CHCH2CH CH2 CH2CH3 CH3 CH2CH3 Substituent alkyl groups at positions 2 & 4 not 4 & 6. c) Name each substituent and indicate its position by the number of the carbon to which it is attached. 1 2 3 4 5 6 7 CH3CHCH2CHCH2 CH2CH3 CH3 CH2CH3 IUPAC name : TPJC/H2 Chem/Intro Organic Chem Part 1/ 8 d) If the parent chain is substituted by the same group more than once, the number of these identical groups is indicated by the prefixes di , tri , tetra and so forth. Br Br H C C CH3 H CH3 IUPAC name : e) If there are two or more substituents, they are named in their alphabetic order. Br e.g 1 2 3 4 CH2CH2CH2 CBr Cl 5 CHCH3 6 CH3 IUPAC name : 1.6 Hybridization Theory : Objective: Candidates should be able to: (c) (e) describe sp3 hybridisation, as in ethane molecule, sp 2 hybridisation, as in ethene and benzene molecules, and sp hybridisation, as in ethyne molecule predict the shapes of, and bond angles in, molecules analogous to those in (d) Table 1.6.1: Summary of Shapes and Bond Angles of Organic Molecules Ethane, C2H6 Ethene, C2H4 Benzene, C6H6 Ethyne, C2H2 H Shape of molecule and type of hybrid orbital of each C atom H H C H H C H H Tetrahedral H around each (sp3) Bond angles Hybridization around C Atomic orbitals of each C atom used in mixing No. of bonds = No. of hybrid orbitals of each C atom No. of bonds = No. of p orbitals of each C atom not involved in hybridisation Total no. of and bonds in molecule H H C C H H H C C C C C C H H H Trigonal planar around each C atom (sp2) Trigonal planar around each C atom (sp2) H C C Linear around each C atom (sp) 109.5 sp3 s, p, p, p 120 sp2 s, p, p 180 sp s, p 4 3 2 0 1 2 7 0 5 1 12 3 3 2 TPJC/H2 Chem/Intro Organic Chem Part 1/ 9 H 1.7 Theory of Hybridization of Carbon Chemical Data of Carbon: Symbol , C Atomic no. = 6 Group IV element Valency of 4 Ground state electronic configuration, 1s 2 2s2 2p2 Ground state electronic configuration: Full electronic configuration: ( show spins of electrons and empty orbitals ) 1s2 1s 2s2 2p2 2s 2px 2py 2pz Hybridization Process 2 step process : Step-1: Excitation State Step-2: Hybridization or Mixing of orbitals Step 1: Excitation State To form four covalent bonds, one electron has to be promoted from the nearest 2s to an empty 2p orbital: C* (excited state) (electronic configuration) 1s 2s 2px 2py 2pz Step 2 :`Mixing` of Orbitals ‘Mixing’ or hybridization of valence shell orbitals takes place at the excited state which gives rise to the following 3 possible outcomes. 1st outcome: 2s + Mixing of (one s and three p) orbitals 2px FOUR identical sp3orbitals 2py 2pz TPJC/H2 Chem/Intro Organic Chem Part 1/ 10 109.5 O Fig. 7 (i) 2nd outcome: + 2s Mixing of (one s and two p) orbitals 2px THREE sp2identical orbitals 2py 2pz (and one unhybridized porbital) p Fig. 7 (ii) sp2 sp2 1200 sp2 3rd outcome: + Mixing of (one s and one p) orbitals 2px 2py 2pz TWO spidentical orbitals (and two unhybridized porbitals) 2s y z Fig. 7 (iii) p sp sp p sp X TPJC/H2 Chem/Intro Organic Chem Part 1/ 11 1.7.1 Formation of Carbon-Hydrogen Single Bonds Objective: Candidates should be able to: (d) explain the shapes of, and bond angles in, the ethane, ethene, benzene, and ethyne molecules in relation to σ and π carbon-carbon bonds -bond formation ( end to end overlapping ) Fig 7.1(a) S sp3– s overlapping ≡ -bond sp3 sp3 sp3 S S sp3 S H sp3-s -bond sp3-s -bond H Fig 7.1(b) sp3-s e.g CH4, methane 1.7.2 C H sp3-s -bond H -bond Formation of Carbon-Carbon Double Bonds Fig 7.2(a) -bond formation side to side p-p overlapping of orbitals -bond p sp2 sp2 sp2 e.g H2CCH2, ethene TPJC/H2 Chem/Intro Organic Chem Part 1/ 12 Fig 7.2(b) H H sp2 – sp2, CC C p – p, H H 1.7.3 Formation of Carbon-Carbon Triple Bonds e.g HC≡CH, ethyne Fig 7.3(a) H s-sp p –p, sp–sp, p –p, CC sp-s C H Checkpoint 1 State the type of hybridization of the carbon atoms, labeled 1 to 5, in the following molecule and hence the geometry (shape) about each of them. 1 5 3 4 2 ----- End of Part 1 -----TPJC/H2 Chem/Intro Organic Chem Part 1/ 13