Chapter 25 Organic Chemistry

25.1 Why Carbon is Different? 25.2 Organic Compounds (groups, functional groups, naming etc.) 25.3 Representing Organic Molecules 25.4 Isomerism 25.5 Organic Reactions (Omitted) 25.6 Organic Polymers (Biopolymer section is omitted)

What is Organic Chemistry? 10.1 Organic chemistry is the field of science that studies the structure, properties, composition of hydrocarbons (compounds containing carbon and hydrogen). These compounds may contain some other elements, including oxygen, nitrogen and halogens. Glucose molecule Fat molecule

Why Carbon is Different 10.1 All known INORGANIC compounds ~100,000 ORGANIC compounds, MILLIONS Electron configuration: [He]2s22p2 shows that C atom effectively prohibits ion formation and tends to share electrons. Carbon atom has a small atomic radius which gives rise to short and strong carbon bonds and, hence, stable compounds. (14Si?? in the same group..) C atoms can form σ and strong π bonds.

These attributes enable carbon to form chains (straight, branched, and cyclic) containing single, double, and triple carbon-carbon bonds. Carbon’s formation of chains is called catenation.

Aromatic Compounds Organic compounds that are related to benzene, or that contain one or more benzene rings, are called aromatic compounds.

Aliphatic Compounds Organic molecules that do not contain the benzene ring are called aliphatic compounds.

10.2 Alkanes Alkanes are simple organic compounds that consist of only carbon and hydrogen. They contain only single bonds. General Formula CnH2n+2 CH4 Methane C2H6 Ethane C3H8 Propane C4H10 Butane C5H12 Pentane

Alkanes General Formula CnH2n+2 C6H14 Hexane C7H16 Heptane C8H18 10.2 Alkanes C6H14 Hexane General Formula CnH2n+2 C7H16 Heptane C8H18 Octane C9H20 Nonane C10H22 Decane

10.2 Alkyl Groups An alkyl group (R) is a portion of a molecule that resembles an alkane. An alkyl group is formed by removing one hydrogen atom from the corresponding alkane. Alkyl groups are represented in organic compounds with R. Methyl Ethyl Propyl Isopropyl

Alkyl Groups 10.2 Butyl tert-Butyl Pentyl Isopentyl Hexyl Heptyl Octyl

Substituents/groups F – Fluoro Cl – Chloro Br – Bromo I - Iodo

Functional Groups 10.2 A functional group is a group of atoms that determines many of the molecule’s properties, and that are responsible for chemical reactions. Some commonly important functional groups: Alcohol Carboxylic acid Aldehydes Esters Ketone Amines Amides

Functional Groups R represents an alkyl group. 10.2 Functional Groups Alcohol Carboxylic acid Ester Aldehyde Ketone R represents an alkyl group. R’ represents a second alkyl group that may or may not be identical to the first alkyl group R.

Functional Groups 10.2 Amine Amine Amine Amide Amide Amide 1, 2 and 3 indicate one, two, and three R groups bonded to the N atom, respectively

Identifying Functional Groups 10.2 R-COOH Carboxylic acid R-NH2 1 amine R-CO-H Aldehyde R-OH Alcohol

Identifying Functional Groups 10.2 Identifying Functional Groups R-CO-R’ Ketone R-COOH Carboxylic Acid

Identifying Functional Groups 10.2

Identifying Functional Groups

Naming Organic Compounds Molecular formula is not enough as the properties of organic compounds vary significantly depending on the group and functional group position.. Hexane (C6H14)

Naming Organic Compounds 10.2 Organic compounds are named using the “International Union of Pure and Applied Chemistry” (IUPAC) rules. There are: Systematic names: names that are based on IUPAC system. Trivial names: names that are commonly used but are not based on IUPAC system. F F Systematic Name Trichloromethane Dichlorodifluoromethane Trivial Name Chloroform Freon

Naming Organic Compounds (Nomenclature) 10.2 How to name alkanes. Identify the longest continuous carbon chain to get the parent name. Number the carbons in the continuous chain, beginning at the end closest to the substituent. Identify the substituent and use a number and a prefix to specify location and identity, respectively. methyl at position 3 hexane 1 2 3 4 5 6 3-Methylhexane

Naming Organic Compounds 10.2 How to name alkanes. When two or more substituents are there: If they are identical, use prefixes (di, tri, tetra, …) to indicates the number of substituents. Also, use numbers as usual to indicate which C atom they are bonded to. methyl 1 2 3 4 5 6 methyl 3,3-Dimethylhexane

3-Ethyl-2-methylhexane 10.2 If the carbon number is same in 2 chains, choose the chain with more substituents How to name alkanes. When two or more substituents are there: If the substituents are not identical, follow the same procedure for identical substituents. However, the substituent names must be put in an alphabetical order. (prefixes are not used to determine the alphabetization) methyl 1 2 3 4 5 6 ethyl 3-Ethyl-2-methylhexane Notice that incorrect numbering would lead to the name 3-isopropylhexane.

Naming Organic Compounds 10.2 Naming Organic Compounds Exercise: Name the following organic compounds: 2-Chloro-3-methylpentane 3-Ethyl-3-methylheptane

Naming Organic Compounds Containing Functional Groups 10.2 How to name alcohols. Identify the longest chain that includes the –OH group. Do numbering such that the C bearing –OH group is given the lowest number. Change the –e ending to -ol. If the chain also contains an alkyl substituent, give the –OH group the lowest number. alcohol 4 3 2 1 1-Butanol Butane 3-Methyl-1-butanol

What we discussed in last lecture Organic chemistry How C is different Aromatic & aliphatic compounds Alkane Alkyl groups & substituents Functional groups Naming organic compounds

Today… Organic Compounds (groups, functional groups, naming etc.) Representing Organic Molecules Isomerism

Containing Carboxy Groups 10.2 How to name carboxylic acids. Identify the longest chain that includes the carboxy group. Do numbering starting with the carbonyl (C=O) carbon. Change the – e ending to – oic acid. Use numbers and prefixes to indicate the position and identity of any substituents. 4 3 2 1 Carboxylic acid Butanoic acid 3 2 1 4 5 3-Fluoro-3-methyl-pentanoic acid

Naming Organic Compounds Containing Functional Groups 10.2 What is the name of the carboxylic acids shown below? Br Ethanoic acid Bromoethanoic acid Acetic acid Bromoacetic acid Trivial name

Naming Organic Compounds Containing Functional Groups 10.2 Ester group How to name esters. Esters are named as derivatives of carboxylic acids by: locating the ester group. locating the main carbon chain which is the R group connected to the C=O group. locating the substituent. replacing the –ic acid ending with – oate. 4 3 2 1 Methyl butanoate Ester group Propyl ethanoate Trivial name Propyl acetate

Naming Organic Compounds Containing Functional Groups 10.2 Aldehyde How to name aldehydes. Identify the longest chain that includes the carbonyl group. Change the –e ending to - al. Number starting with the carbonyl (C=O) carbon. Use numbers and prefixes to indicate the position and identity of any substituents. 3 2 1 Propanal 1 2 3 4 5 2,5-Dichloro-2-ethylpentanal

Naming Organic Compounds Containing Functional Groups 10.2 Naming Organic Compounds Containing Functional Groups How to name ketones. Identify the longest chain that includes the carbonyl group. Number to give the carbonyl group (C=O) the lowest possible number. Change the –e ending to - one. Use numbers and prefixes to indicate the position and identity of any substituents. Carbonyl 4 3 2 1 2-Butanone 4 5 6 7 8 3 2 1 8-Iodo-2-methyl-4-octanone

Naming Organic Compounds Containing Functional Groups 10.2 Amine How to name primary amines. Identify the longest chain that includes the –NH2 group. Number C atoms so that the C atom to which the –NH2 group is bonded is given the lowest possible number. Change the –e ending to - amine. Use numbers and prefixes to indicate the position and identity of any substituents. 2 1 Ethanamine 5 4 3 2 1 1-Pentanamine 5 4 3 2 1 1,5,5-Trichloro-2-pentanamine

Naming Organic Compounds Containing Functional Groups 10.2 Amide How to name primary amides. Primary amides can be named as derivatives of carboxylic acids by replacing the –ic acid ending with – amide. 3 2 1 Propanamide 6 5 4 3 2 1 4-Fluoro-5-methylhexanamide

Naming Organic Compounds 10.2 Naming Organic Compounds Exercise: 4 5 6 7 4 5 8 1 2 3 3 6 9 2 7 10 8 1 4-ethyl-7-methyl-5-propyldecane 4-ethyl-5-propyloctane

Representing Organic Molecules Condensed Structural Formulas Kekulé Structures Skeletal Structures Resonance

Representing Organic Molecules Condensed Structural Formulas A condensed structural formula, or simply a condensed structure, shows the same information as a structural formula, but in a condensed form.

Representing Organic Molecules Condensed Structural Formulas

Representing Organic Molecules 10.3 Representing Organic Molecules Kekulé structure Kekulé structure: It is similar to Lewis structure but without showing the lone pairs. It is very commonly used in organic chemistry. Kekulé structure

Representing Organic Molecules Kekulé structure

Representing Organic Molecules Skeletal structure

When a heteroatom is present? Skeletal structure

Representing Organic Molecules 10.3 Exercise: Write a molecular formula and condensed structural formula for the following: C4H8 C2H5NO Molecular formula Molecular formula CH3(CH)2CH3 CH3CONH2 Cond. Structural formula Cond. Structural formula

Representing Organic Molecules 10.3 Exercise: Write the molecular formula and a structural formula for the following molecule. O CH3COCH2CH3 Structural formula C4H8O Molecular formula What is the correct name of this compound? 2-butanone

10.3 Resonance Resonance is repositioning of electrons to produce other equivalent structures of the molecule. You will need to review how to draw Lewis structures for simple organic compounds. Example: Draw the Lewis structure of nitrate ion (NO3‒) and show resonance structure. N 1– O

10.3 Resonance The nitrate ion structure is the average of all the three equivalent structures, not one of them. The three NO bonds are found from experiments to be identical. Resonance structures: 1– 1– 1– O O O N N N O O O O O O

More Examples on Resonance Structures 10.3 More Examples on Resonance Structures The anion produced from ethanoic acid (ethanoate). Benzene molecule (C6H6)

Why acetic acid loses protons much more easily than alcohol??

ISOMERISM Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space. Excludes any different arrangements which are simply due to the molecule rotating as a whole, or rotating about particular bonds.

Constitutional or Structural Isomerism 25.4 ISOMERISM Constitutional or Structural Isomerism Stereoisomerism Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 52

ISOMERISM 25.4 Constitutional Isomerism Constitutional isomerism occurs when the same atoms can be connected in two or more different ways. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 53

ISOMERISM 25.4 Constitutional Isomerism 54 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 54

How many structural isomers hexane (C6H14) has, draw the structure?

ISOMERISM Stereoisomerism Stereoisomers are those that contain identical bonds but differ in the orientation of those bonds in space. Two types of stereoisomers exist: geometrical isomers and optical isomers. Geometrical isomers occur in compounds that have restricted rotation around a bond. Stereoisomers that are mirror images of each other, but are not superimposable, are called optical isomers. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 56

ISOMERISM 25.4 Stereoisomerism (Geometrical Isomerism) Structural isomer Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 57

ISOMERISM 25.4 Stereoisomerism (Optical Isomerism) 58 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 58

ISOMERISM 25.4 Stereoisomerism (Optical Isomerism) Molecules with nonsuperimposable mirror images are called chiral; and a pair of such mirror-image molecules are called enantiomers. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 59

25.4 ISOMERISM Representing three-dimensional objects on two-dimensional surface it often is necessary to represent tetrahedral molecules (three- dimensional objects) on paper (a two-dimensional surface). This is done using dashes to represent bonds that point behind the page, and wedges to represent bonds that point in front of the page. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 61

ISOMERISM 25.4 Determination of chirality or enantiomers One property of chiral molecules is that the two enantiomers rotate the plane of plane-polarized light in opposite directions; that is, they are optically active. If the plane of polarization is rotated to the right, the isomer is said to be dextrorotatory and is labeled d; if it is rotated to the left, the isomer is called levorotatory and labeled l. Enantiomers always rotate the light by the same amount, but in opposite directions. Thus, in an equimolar mixture of both enantiomers, called a racemic mixture, the net rotation is zero. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 62

25.4 Isomerism Stereoisomerism 63 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 63

Condensation Polymers Addition Polymers Condensation Polymers

25.6 Organic Polymers Addition Polymers Polymers are molecular compounds, either natural or synthetic, that are made up of many repeating units called monomers. Addition polymers form when monomers such as ethylene join end to end to make polyethylene. Reactions of this type can be initiated by a radical—a species that contains an unpaired electron. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 65

25.6 Organic Polymers Addition Polymers 66 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 66

25.6 Organic Polymers Addition Polymers 67 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 67

25.6 Organic Polymers Addition Polymers 68 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 68

25.6 Organic Polymers Condensation Polymers Reactions in which two or more molecules become connected with the elimination of a small molecule, often water, are called condensation reactions. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 69

25.6 Organic Polymers Condensation Polymers Condensation polymers form when molecules combine through functional groups with the elimination of a small molecule, often water. Many condensation polymers are copolymers, meaning that they are made up of two or more different monomers. Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 70

25.6 Organic Polymers Condensation Polymers 71 Copyright © 2014, The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 71

Exercise Draw the structure of polypropylene, showing atleast 2 repeating units. Draw the structure of monomer used to make the below polymer. Polymethyl methacrylate

Draw the structure of monomer used to make the below polymer.

Answers monomer n monomer

Answers monomer monomer polymer