CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 1 | P a g e CHAPTER 1 : INTRODUCTION TO ORGANIC CHEMISTRY INTRODUCTION TO ORGANIC CHEMISTRY 1.1 Introduction Identify the elements that made up organic compounds. 1.2 Structural Formula Define structural formula Condensed structure, expanded structure, skeletal structure Primary carbon, secondary carbon, tertiary carbon, quarternary carbon Primary hydrogen, secondary hydrogen, tertiary hydrogen 1.3 Classification of Organic Compound Define functional group Name functional group Classify organic compound according to their functional group. Define and explain homologous series Single bond, double bond and triple bond 1.4 Hydrocarbon Define hydrocarbons Classify hydrocarbon into aliphatic, aromatic, saturated and unsaturated Differentiate between saturated and unsaturated of organic compound 1.5 Isomerism Classify and draw the constitutional isomers: chain, positional and functional group isomers. 1.6 Basic reaction in organic compound Homolytic and heterolytic cleavage Define and stability of free radical and carbocation. Type of organic reactions: substitution,addition and elimination reaction.
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 2 | P a g e 1.1 Introduction to Organic Chemistry Organic chemistry is the branch of chemistry that deals with of carbon compounds. Organic compounds are considered to be those that contain carbon and hydrogen, while other common elements are O, N, the halogens, S and P. Examples of carbon compounds in our daily lives :- Methane C H H H H • The simplest organic compound • One of primary energy resource glucose O OH H H H HO H OH OH H OH • Principal sugar in blood Urea C NH2 O H2N • Use in urea–formaldehyde resins, pharmaceuticals, and as a nitrogen fertilizer DDT (Dichlorodiphenyltrichloroethane) CH C Cl Cl Cl Cl Cl • Used as an insecticide Penicillin CH2 C NH O N O S CH3 CH3 • An antibiotic derived from the mould Penicillium notatum Nicotine N N CH3 • A colorless poisonous alkaloid presents in tobacco
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 3 | P a g e Cafeine N N N O CH3 CH3 O H3C • Stimulant in coffee, tea, and many soft drinks DNA (Deoxyribonucleic acid) Genetic information is stored as a sequence of nucleotides EXERCISE 1 Identify which of the following compounds are ORGANIC COMPOUND? a) C6H5NH3Cl b) (NH4)2SO4 c) Na2CO3 d) HCl e) CH2═CHCH3 f) CH3CH2COCl g) HNO3 1.2 Structural formula Structural Formula is a formula that shows how the atoms of a molecule are bonded to each other.
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 4 | P a g e Structural formula can be drawn in the form of condensed, expanded and skeletal structure. i) Condensed Structure In condensed formulae all the hydrogen atoms that are attached to a particular carbon are usually written immediately after that carbon, In fully condensed formulae all atoms that are attached to a carbon are written immediately after that carbon Example : C4H9Cl CH3CH(Cl)CH2CH3 ii) Expanded Structure Expanded structures indicate the way in which the atoms are attached to each other and are not representations of the actual shapes of the molecules. Example : iii) Skeletal Structure This structure shows only the carbon skeleton • C chains are drawn zigzag, and rings are drawn as polygons The hydrogen atoms that are assumed to be present, are not written. Other atoms such as O, Cl, N and etc. are shown. Examples : i) CH3CH(Cl)CH2CH3 = ii) iii) CH2 = CHCH2 OH = EXERCISE 2 1. Convert each molecule into expanded structure. a) (CH3)2CHCH2CH2CH(CH3)2 b) CH3CH(Cl)CH(OH)CH3 C C C C H H H Cl H H H H H H H2C CH2 H2C CH2 Cl Expanded structure OH C4H9Cl =
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 5 | P a g e 2. Write a condensed structural formula for each of the following compounds. a) b) c) d) Classification Of Carbon And Hydrogen Atoms In Organic Molecules A carbon atom is classified as primary (1o ), secondary (2o ), tertiary (3o ) or quarternary (4o ) depending on the number of carbon atoms bonded to it. ▪ a primary carbon is directly bonded to one other carbon atom (has 1 adjacent carbon atom). ▪ a secondary carbon is directly bonded to two other carbon atoms (has 2 adjacent carbon atoms). ▪ a tertiary carbon is directly bonded to three other carbon atoms (has 3 adjacent carbon atoms) . ▪ a quarternary carbon is directly bonded to four other carbon atoms (has 4 adjacent carbon atoms).
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 6 | P a g e Similarly, a hydrogen atom is also classified as primary, secondary or tertiary depending on the type of carbon to which it is bonded. ▪ 1 o hydrogen atom is bonded to a 1o carbon atom. ▪ 2 o hydrogen atom is bonded to a 2o carbon atom. ▪ 3 o hydrogen atom is bonded to a 3o carbon atom. KEEP IN MIND! No classification for C atoms in methane and in multiple bonds Only for sp3 C atom EXERCISE 3 Identify the types of carbons (1o , 2o , 3o , or 4o ) in the following molecules. Label at each C atom. a) CH3 CH CH2 CH3 CH3 b) CH3 c) d)
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 7 | P a g e 1.3 Classification of organic compounds Functional group is an atom or group of atoms that imparts characteristic chemical properties to an organic compound. Identifying and classifying functional groups of different class of compounds: Class of compounds Functional Group Example Structure Name Alkane CnH2n+2 None - CH3CH3 Alkene CnH2n C C Carbon-carbon double bond CH2=CH2 Alkyne CnH2n-2 C C Carbon-carbon triple bond CHCH Aromatic/Arene CnHn Aromatic ring Alcohol CnH2n+2O -OH Hydroxyl CH3CH2OH Haloalkane CnH2n+1X -X (F,Cl,Br,I) Halogen CH3CH2Cl Ether CnH2n+2O C O C Alkoxy CH3OCH3 Aldehyde CnH2nO C O H Carbonyl CH3CHO Ketone CnH2nO C O R R Carbonyl CH3COCH3 Carboxylic acid CnH2nO2 C O OH Carboxyl CH3COOH Ester CnH2nO2 C O O R Carboalkoxy/ ester CH3COOCH3 Acyl chloride CnH2n+1COCl C O Cl Acyl CH3COCl Anhydride (CnH2n+1CO)O C O O C O Anhydride CH3COOCOCH3 Amide CnH2n+1CONH2 C O N Carboxamide/ amide CH3CONH2 Amine CnH2n+1NH2 C N Amino CH3NH2 Nitrile CnH2n+1CN C N Cyano CH3CN
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 8 | P a g e EXERCISE 4 Identify the functional groups in the following molecules. a) CH3 C CH3 CH2 CH3 C NH2 O b) CH3 c) CH3 O CH2CH3 d) CH2CH3 e) H3C C O OCH2CH3 f) OH H2N O Br O O HO g) O O CH2CH2OH CH2COOH H2N
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 9 | P a g e h) C O H OCH3 OH i) HN C C N C C OH H3C C O O H H H H H H H Homologous series Homologous series is a series of compounds with the same functional group where each member of the series differs from the next member by a constant – CH2 unit. Members of the same homologous series are called homologs. General Characteristics of homologous series. There are four features of homologous series: 1. All the members of a particular homologous series share the same general formula. Example: Homologous series of alcohol General formula: CnH2n+1OH, where n=1, 2, 3, etc. Functional group: hydroxyl (OH) Structure Name n = 1 CH3OH Methanol n = 2 CH3CH2OH Ethanol n = 3 CH3CH2CH2OH 1-propanol *Methanol, ethanol and 1-propanol are said as members of homologous series. 2. All members of a particular homologous series have the same functional group and same chemical properties. Example: ▪ All alcohols contain the -OH group ▪ They react with carboxylic acids to give esters
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 10 | P a g e ▪ The can be prepared by heating dilute sodium hydroxide solution with anappropriate alkyl halide. 3. Successive member of a series differs by a –CH2 unit Example: ALKANES CH4 Methane CH3CH3 Ethane CH3CH2CH3 propane *each member differ by CH2 ALDEHYDE HCHO Methanal CH3CHO Ethanal CH3CH2CHO Propanal *each member differ by CH2 4. Each member of a homologous series gradually change in physical properties with increasing number of carbon atoms. Example: PHYSICAL PROPERTIES Compound Boiling point CH4 -162 oC CH3CH3 -88.2oC As number of carbons increase, size of molecule becomes larger, boiling and melting point increase. General Formula Homologous Series SERIES GENERAL FORMULA ENDING NAME Alkane CnH2n+2 …ane Alkene CnH2n …ene Alkyne CnH2n-2 …yne Alcohol R-OH …ol Aldehyde R-CHO …al Ketone R-COR’ …one Carboxylic acid R-COOH …oic acid Amine R-NH2 …amine Amide R-CONH2 …amide *R normally refer to alkyl group: CnH2n+1 *reduce 2 atom H for cyclic compound
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 11 | P a g e Homologous series of alkyl group Alkane CnH2n+2 Alkyl CnH2n+1 Methane CH4 Methyl -CH4 Ethane CH3CH3 Ethyl -CH2CH3 Propane CH3CH2CH3 Propyl -CH2CH2CH3 Butane CH3CH2CH2CH3 Butyl -CH2CH2CH2CH3 Pentane CH3CH2CH2CH2CH3 Pentyl -CH2CH2CH2CH2CH3 Homologous series of cycloalkanes Alkane CnH2n+2 Cycloalkane CnH2n Methane CH4 - - Ethane CH3CH3 - - Propane CH3CH2CH3 Cyclopropane Butane CH3CH2CH2CH3 Cyclobutane Pentane CH3CH2CH2CH2CH3 Cyclopentane Homologous series of alkenes and cycloalkenes Alkane CnH2n Cycloalkane CnH2n-2 Ethene CH2=CH2 - - Propene CH2=CHCH3 Cyclopropene Butene CH2=CHCH2CH3 1-butene CH3CH=CHCH3 2-butene Cyclobutene Pentene CH2=CHCH2CH2CH3 1-pentene Cyclopentene KEEP IN MIND! Alkanes and cycloalkanes belong to the same class of compound but different homologous series. Ability of carbon to form 4 covalent bonds with other carbons or elements: C atom can form four covalent bonds with other C or elements: ▪ Single bond (EXAMPLE: C‒C, C‒X)
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 12 | P a g e ▪ Double bond (EXAMPLE: C=C, C=O) ▪ Triple bond (EXAMPLE: C≡C, C≡N) 1.4 Hydrocarbons • Hydrocarbons are compound composed of only carbon and hydrogen. Examples: (aliphatic) (aromatic) (aliphatic) (saturated) (unsaturated) (saturated) ▪ Aliphatic hydrocarbon are composed of straight-chained, branched or cyclic compounds and can be saturated (alkanes) or unsaturated (alkenes and alkynes). ▪ Aromatic hydrocarbon have one or more conjugated, benzene or heterocylic rings within their structures. “Conjugated” refers to the presence of delocalized (shared) electrons within the chemical structure, such as benzene or arenes. ▪ Compounds such as the alkanes and cycloalkanes, whose molecules contain only single bonds are referred to as saturated hydrocarbons. They contain the maximum number of hydrogen atoms that the carbon compound can possess. ▪ Compounds with multiple bonds such as alkenes, cycloalkenes, alkynes and aromatic hydrocarbons are called unsaturated hydrocarbons. They posses fewer than the maximum number of hydrogen atoms. Example: Aliphatic hydrocarbon Aromatic hydrocarbon CH4 methane benzene
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 13 | P a g e cyclohexane CH2 CH3 ethylbenzene CH3CH=CH2 propene naphthalene Saturated hydrocarbon -contains only single bond Unsaturated hydrocarbon -contains double or triple bond CH4 methane CH3CH=CH2 propene cyclohexane CH3CCH propyne CH3CH2CH3 propane benzene 1.5 Isomerism Isomerism is the existence of different compounds with the same molecular formula but different structural formulae. Different compounds that have the same molecular formula are called isomers. Structural isomers are different compounds with the same molecular formula but differ in the order of attachment of atoms. Three types of structural isomerism :- a) Chain isomerism The isomers differ in the carbon skeleton (different carbon chain). They possess the same functional group and belong to the same homologous series. Example: How many structural isomers does pentane, C5H12, have? • CH3CH2 CH2CH2 CH3 n-pentane • CH3CH CH2CH3 CH3 isopentane
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 14 | P a g e • CH3C CH3 CH3 CH3 neopentane There are three isomers of C5H12. All the three isomers are chain isomers of each other due to different in carbon skeleton. b) b) Positional isomerism These isomers have a substituent group in different positions in the same carbon skeleton. Example : Molecular formula: C3H7Cl CH3CH2CH2Cl CH3CH CH3 Cl 1-chloropropane 2-chloropropane Molecular formula: C4H8 CH2=CHCH2CH3 CH3CH=CHCH3 1-butene 2-butene c) Functional group isomerism These isomers have different functional groups and belong to different homologous series with the same general formula. Different classes of compounds that exhibit functional group isomerism :- General formula Classes of compounds CnH2n+2O alcohol and ether CnH2nO aldehyde and ketone CnH2n alkene and cycloalkane CnH2nO2 carboxylic acid and ester Examples : C2H6O: CH3CH2OH and CH3OCH3 ethanol dimethyl ether C3H6O: CH3CH2CHO and CH3COCH3 propanal propanone C3H6O2: CH3CH2COOH and CH3COOCH3 propanoic acid methyl ethanoate
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 15 | P a g e EXERCISE 5 Draw all structural isomers of compound with the molecular formula; a) C4H10O b) C4H8O c) C4H8 1.6 Basic reaction in organic compounds a) Types of Covalent Bond Cleavage/Fission All chemical reactions involved bond breaking and bond making. Two types of covalent bond cleavage :- ▪ Homolytic cleavage ▪ Heterolytic cleavage i) Homolytic Cleavage Occurs in a non-polar bond involving two atoms of similar electronegativity. A single bond breaks symmetrically into two equal parts, leaving each atom with one unpaired electron. Free radicals are formed in homolytic cleavage. X : X X. + X. free radicals ii) Heterolytic cleavage Occurs in a polar bond involving unequal sharing of electron pair between two atoms of different electronegativities. A single bond breaks unsymmetrically and both the bonding electrons are transferred to the more electronegative atom. Cation and anion are formed in heterolytic cleavage. A:- + B+ anion cation A : B A+ + B:- cation anion Carbocations and free radicals are intermediates in organic reactions. They are unstable and highly reactive. A is more electronegative . B is more electronegative
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 16 | P a g e b) Reaction Intermediates i) Carbocation Also called carbonium ion. A very reactive species with a positive charge on a carbon atom. Carbocation is formed in heterolytic cleavage. Example : + − (CH3)3C — Cl (CH3)3C+ + Cl- carbocation anion Chlorine is more electronegative than carbon and the C—Cl bond is polar. The C—Cl bond breaks heterolitically and both the bonding electrons are transferred to chlorine atom to form anion and carbocation. ii) Free Radical A very reactive species with an unpaired electron. Formed in homolytic cleavage. Example: free radicals X : X X. + X. C C C + C H3C H CH3 + H c) Relative Stabilities of Carbocations and Free Radicals Carbocation and free radical can be primary, secondary or tertiary, depending on the number of carbon atoms directly bonded to the :- positively charged carbon atom ( for carbocation ) carbon atom with unpaired electron ( for free radical ) The stability of carbocation increases with the number of alkyl groups present. The alkyl groups are electron-releasing relative to hydrogen, thus help to stabilize the positive charge on the carbocation. As the number of alkyl groups attached to the positively charged carbon atom increases, the stability of carbocation increases.
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 17 | P a g e i)Carbocation Stability: methyl primary secondary tertiary cation (1o ) (2o ) (3o ) Increasing stability Likewise, the stability of free radical increases as more alkyl groups are attached to the carbon atom with unpaired electron. ii) Free Radical Stability : methyl primary secondary tertiary radical (1o ) (2o ) (3o ) Increasing stability d) Types of Organic Reactions The four main types of organic reactions are: i. Addition reaction ii. Substitution reaction iii. Elimination reaction iv. Rearrangement Reaction I) Addition Reaction A reaction in which atoms or groups add to adjacent atoms of a multiple bond. Two types of addition :- a) Electrophilic Addition Reaction Initiated by an electrophile, which attacks a nucleophilic site of a molecule. Typical reaction of unsaturated compounds such as alkenes and alkynes. Example : room CH3CH=CH2 + Br2 CH3CH(Br)CH2Br electrophile temperature H C H < R C H < R C H < R C R H H R R H C H < R C H < R C H < R C R H H R R + + + +
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 18 | P a g e b) Nucleophilic Addition Reaction Initiated by a nucleophile, which attacks an electrophilic site of a molecule. Typical reaction of carbonyl compounds. Example : − II) Substitution Reaction A reaction in which an atom or group in a molecule is replaced by another atom or group. Three types of substitution :- a) Free-radical Substitution Reaction Substitution which involves free radicals as intermediate species. Example : uv light CH3CH3 + Cl2 CH3CH2Cl + HCl b) Electrophilic Substitution Reaction Typical reaction of aromatic compounds. The aromatic nucleus has high electron density, thus it is nucleophilic and is prone to electrophilic attack. Example : + Br Br Br + HBr FeBr3 electrophile c) Nucleophilic Substitution Reaction Typical reaction of saturated organic compounds bearing polar bond as functional group, such as haloalkane and alchohol. Example : + − CH3CH2Br + OH- (aq) CH3CH2OH + Br- (aq) nucleophile + CH3 C CH 3 + HCN O CH3 C CH3 OH CN nucleophile
CHAPTER 1: INTRODUCTION TO ORGANIC CHEMISTRY | CHEMISTRY UNIT KMKt 2021/2022 19 | P a g e III) Elimination Reaction A reaction in which atoms or groups are removed from adjacent carbon atoms of a molecule to form a multiple bond (double or triple bond). Elimination reaction results in the formation of unsaturated molecules. Example : conc. H2SO4 CH3CH2OH CH2= CH2 + H2O IV) Rearrangement Reaction A reaction in which atoms or groups in a molecule change position. Occurs when a single reactant reorganizes the bonds and atoms. Example : H C C H OH R C C H H O R H tautomerisme EXERCISE 6 State the type of reaction for the following reaction. a) CH3Br + KOH → CH3OH + KBr b) CH3CH2OH → H2C═CH2 + H2O c) H2C═CH2 + H2 → CH3CH3 Prepared by: Revised by: ELMI SHARLINA BINTI MD SUHAIMI ZANARINA BINTI SAPIAI