Organic Chemistry

Organic Chemistry

Organic Chemistry Syed Arshad Mushtaq ESSENTIAL IDEA Organic chemistry focuses on the chemistry of compounds containing carbon. NATURE OF SCIENCE (1.4) Serendipity and scientific discoveries PTFE and super glue. NATURE OF SCIENCE (4.5) Ethical implications drugs, additives and pesticides can have harmful effects on both people and the environment. INTERNATIONAL-MINDEDNESS A small proportion of nations have control over

the worlds oil resources. The interdependence of the countries that are net importers and those that are next exporters is an important factor in shaping global policies and economic developments. The octane rating (octane number) can be described as a standard measure of the performance of the fuel used in cars and aircraft. Octane ratings often vary quite widely regionally throughout the globe, and are complicated by the fact that different countries use different means of expressing the values. THEORY OF KNOWLEDGE The label organic chemistry originates from a misconception that a vital force was needed to

explain the chemistry of life. Can you think of examples where vocabulary has developed from similar misunderstandings? Can and should language ever be controlled to eliminate such problems? UNDERSTANDING/KEY IDEA 10.1.A A homologous series is a series of compounds of the same family, with the same general formula, which differ from each other by a common structural unit. HOMOLOGOUS SERIES

Definition family of organic compounds which possesses certain common features. Successive members differ by a CH2 group. Members of a series can be represented by the same general formula. Members show a gradation in physical properties. Members have similar chemical MEMBERS DIFFER BY CH2 In a homologous series, as you

change from one member to the next, the molecular mass increases by a fixed amount. This fixed amount is due to the addition of successive CH2 groups. When you go from propane to butane, what changed? You added one carbon to the series along with two hydrogen atoms. This is typical of each homologous series. MEMBERS REPRESENTED BY SAME GENERAL FORMULA

Alkanes and alkenes are represented by the formulas CnH2n+2 and CnH2n respectively. A functional group is a small group of atoms attached to a carbon atom giving the compound characteristic properties. Functional groups are shown in the general formulas. Alcohols are represented by CnH2n+1OH or ROH where R is the parent MEMBERS SHOW A GRADATION OF PHYSICAL PROPERTIES As successive members of a series differ

by a CH2 group, they have successively longer chains. There is a gradual trend in the change of physical properties due to this change in molar mass. Boiling point, density and viscosity are physical properties with predictable trends in homologous series. MEMBERS SHOW SIMILAR CHEMICAL PROPERTIES. Since members of a series have the same functional group, their members show similar chemical reactivity. If we know the characteristic reactions of

a functional group, we can predict the properties of all members of a series. Examples of homologues series Alkene Alcohol CH3OH Methanol C2H4 Ethene C2H5OH Ethanol

C3H6 Propene C3H7OH Propanol C4H8 Butene C4H9OH Butanol

C5H10 Pentene C5H11OH Pentanol Hexene C6H13OH Hexanol C6H12 APPLICATION/SKILLS

Be able to explain the trends on boiling points of members of a homologous series. BOILING POINT TRENDS The boiling point is affected by the length of the carbon chain. Boiling point increases with increasing carbon number. This is caused by the increased number of temporary dipoles causing stronger van der Waals forces between molecules as their size increases. The first four alkanes are gases at room

temperature followed by the next four alkanes existing as liquids at room temp. Methane has a boiling pt of -164C and octane 125C. The increase is not linear, but steeper near the beginning because the smaller molecules are more affected by the addition of a CH2. APPLICATION/SKILLS Be able to distinguish between empirical, molecular and structural formulas. EMPIRICAL FORMULA

Definition the simplest whole number ratio of the atoms a compound contains. The formula can be derived from percentage composition data obtained from combustion analysis. It is limited in its use as it does not tell us the actual number of atoms in the molecule. MOLECULAR FORMULA Definition the actual number of atoms of each element present in the compound and is a multiple of the empirical formula. It does not show us how the atoms are arranged in relation to each other and in

space. Properties of a compound are determined by not only the atoms, but by their arrangement in space so the molecular formula is limited in its value. UNDERSTANDING/KEY IDEA 10.1.B Structural formulas can be represented in full and condensed format. STRUCTURAL FORMULA A full structural formula shows us every bond and every atom. H

H H-CCH H H You must show all Cs and Hs and functional groups in a structural formula or you will not receive credit. Skeletal structures are not acceptable. CONDENSED STRUCTURAL FORMULA A condensed structural formula omits bonds where they can be assumed and

groups atoms together. CH3CH3 or CH3COOH STEREOCHEMICAL FORMULA Attempts to show the positions of atoms in three dimensions. A bond sticking out of the front of the page is represented by a solid triangular wedge. A bond sticking out of the back of the page is dotted line. Four bonds are tetrahedral with bond angles of 109.5.

Three bonds are trigonal planar with 120. Understanding/Key idea Structural isomers are compounds with the same molecular formula but different arrangements of atoms Structural Isomers Structural isomers are different compounds with the same molecular formula but different arrangements of atoms Butane C4H10

Try Structural formula for C5H12 C5H10 ( hint one double) UNDERSTANDING/KEY IDEA 10.1.C Saturated compounds contain single bonds only and unsaturated compounds contain double and triple bonds. GUIDANCE Be able to apply the IUPAC rules in nomenclature for the following:

1. non-cyclic alkanes and halogenoalkanes up to halohexanes 2. alkenes up to hexene 3. alkynes up to hexyne GUIDANCE 4. Compounds up to 6 carbon atoms containing only one of the classes of functional groups: alcohols, ethers, aldehydes, halogenoalkanes, ketones, esters, and carboxylic acids, amines, Learning out come Identify the following different classes:

alkanes, alkenes, alkynes, halogenoalkanes, alcohols, ethers, aldehydes, ketones, esters, carboxylic acids, amines, amides, nitriles and arenes Identify typical functional groups in molecules e.g. phenyl, hydroxyl, carbonyl, carboxyl, carboxamide, aldehyde, ester, ether, amine, nitrile, alkyl, alkenyl and alkynyl. Its Family thing UNDERSTANDING/KEY IDEA 10.1.D Functional groups are the reactive parts of molecules. Definition : An atom or group of atoms that give characteristic properties to an organic compound

Picture Source https://www.pinterest.com/pin/199073245998510273 / Nitrile Example Butanenitrile Identify functional groups Alcohol Ether Identify functional groups in Acetylsalicylic acid

Carboxylic acid group (Aspirin ) Ester Group A B C D Nomenclature System of Naming Learning outcomes Should be able to name Non-cyclic alkanes and halogenoalkanes

containing up to six carbon atoms. Alkenes up to hexene and alkynes up to hexyne. Compounds up to six carbon atoms (in the basic chain for nomenclature purposes) containing only one of the following functional groups: hydroxyl, ether, aldehyde, halogenoalkane, carbonyl, ester and carboxyl. Naming Organic Compounds Originally compounds were named based on their source or use Many organic compounds were given common names which are still in use However many ambiguities resulted

With the large number of organic compounds, a method for systematically naming them is very important 38 IUPAC Names The International Union of Pure and Applied Chemists (IUPAC) developed a system for naming organic compounds. This system eliminated many of the ambiguities that plagued earlier naming systems Common names for many substances are still widely used 39

Naming Hydrocarbons using the IUPAC System A series of prefixes are used to designate the number of carbon atoms in a carbon chain meth 1C hex 6C eth 2C hept 7C

prop 3C oct 8C but 4C non 9C pent

5C dec 10 C 40 Naming Alkanes For straight chain hydrocarbons. The prefix indicates the number of carbon atoms. The suffix ane is added to designate that the compound is an alkane

41 Naming Alkanes with branched chains For branched chain hydrocarbons, identify the longest consecutive (straight) chain first. Then name the side chains or branches. The name of the branches end in yl and go before the name of the straight chain -methylpropane methyl butane

dimethyl propane Video 42 Practice 2- methyl H H C H H H

C C H H C H H H H

H C C C C H H H H

H Hexane H 2- methyl 2-methyl, 2-methyl hexane Sounds redundant 2,2 dimethyl hexane Practice H H

C H H H H H C C H C

C C H H H H H C H

H 2,3-Dimethyl hexane H 2-methyl hexane Is your arm sore yet? Are you sick to death of writing all those carbons? Even worse, are you sick of writing all those Hydrogens? How about this

Shorthand notation H H H H H C C C

C H H H H H Keep in mind that we have been ignoring the hydrogens for a long time. Our names have been based entirely on the positioning of the carbons.

So lets now ignore the hydrogens completely! Is it that easy? H H H H H H

H H C C C C C C

C H H H H H H C H

H H H H H H H H C

C H H C H H H H H

H C C C C C C H

H H H H H C H H H Alkenes

Alkenes have one (or more) carbon to carbon double bonds When there are 4 or more carbon atoms in a chain, the location of the double bond is indicated by a number. Numbering the location of the double bond(s) takes precedence over the location of side chains but-1-ene but-2-ene

2-methylpropene 48 Practice H H H H H C

C C C C C H H H

H H H H H H H H C

C C C H H H hex-2-ene but-1-ene H

H H H C H H C C C

H H H H H H C C H

3 methyl pent-1-ene How about in Shorthand? 3-methylpent-1-ene, Notice the two lines means the double bond is there! pent-2-ene 2,3-dimethylbut-2-ene, Practice! Methyl propene 2,4-dimethylpent-2-ene

3-ethyl-2,4,4-trimethylpent-1-ene Geometric Isomers in alkenes A cis isomer is one in which the substituents are on the same side of the C=C cis-but-2-ene A trans isomer is one in which the substituents are on the opposite sides of the C=C trans-but-2-ene

52 cis isomers have higher boiling point than trans. trans pent-2ene 2,3-dimethylbut-2-ene does not have geometrical isomers because there are two identical groups attached to the same carbon of the double bond. Alkynes Alkynes have one (or more) carbon to carbon triple bonds

Since there are fewer hydrogen atoms in alkynes as a result of the triple bond, alkynes like alkenes are referred to as unsaturated. 55 Alkyne Structures Like alkanes and alkenes, alkynes can have branched or consecutive chains. In the larger alkenes there are also multiple locations for the C=C. Multiple structural isomers are possible. The branch cannot originate on one of the carbons making up the triple bond

Straight chain. The triple bond is between the first and second carbon Straight chain. The triple bond is between the second and third carbon Branched chain. The triple bond can occur in one of the branches but branches cannot be attached to any 56 carbon in the triple bond

Practice Draw the structure of the followings 2-Methyl pent-1-yne hex-2-yne 4,4-Dimethyl Practice This one Pentyne Head-to-Head Naming Draw a hydrocarbon molecule on a sheet. Have a friend draw a hydrocarbon

molecule on their sheet. Exchange papers and see who can correctly name the other persons hydrocarbon first. As always, no wagering please. For more lessons, visit Halogenoalkane Fluorides, Chlorides, Bromides, and Iodides attached to Alkyl group Simply name the molecule as normal but add the prefix

Fluoro, Chloro, Bromo, or Iodo as necessary Halogenoalkane 1-bromopropane 2 chlorobutane prefixes = fluoro, chloro, bromo, iodo 1,2 diiodoethane cis 1,2difluroethene Trans 1,2 difluoroethene

1,1,2 trifluorothene 62 Halogenoalkane Cl 2, 3 dichlorohexane Cl I 3, 3 diiodopent-1-ene I Worksheets Timer

TOK Connection Functional Groups Halogenoalkanes Alcohols Ethers Aldehydes Ketones Carboxylic Acids Esters Amines R-F, R-Cl, R-Br, R-I R-OH R-O-R R-COH

R-CO-R R-COOH R-COO-R R-NH2 Naming Compounds With Functional Groups Various functional groups have unique suffixes that designate the functional group. The functional group takes precedence in numbering the carbon chain. Branches to the carbon chain are named in the usual manner. alcohols ol

Amides amide Aldehydes al Amines amine or amino as a prefix Ketones one Ethers

Ethoxy as prefix Acids oic halohydrocarbons Fluoro, bromo, chloro or iodo Esters oate 67

Alcohols R-OH Name like normal except add an ol suffix Alcohols Propan-1-ol Suffix = ol Propan-2-ol 2-methyl propan-2-ol 69

OH Alcohols Propan-2ol H H H C C H

H OH cyclobutanol OH ethanol Ethers R-O-R Name two R groups with yl endings End name in ether

Ethers Suffix = oxyon first branch Ethoxyethane (diethylether) Ethoxybutane (ethylbutyl ether) 72 Ethers O O Dimethyl ether

(Methoxymethane) Ethyl methyl ether (Methoxyethane) Aldehyde R-CHO This is a carbon to oxygen double bond with a hydrogen at the end. Name as normal except use a -al suffix

Aldehydes and Alkanals Suffix = al Propanal Note that the aldeyhde group is always on an end carbon or carbon 1 75 Aldehydes H H

H H H O C C C C H

H H H H Cl H O C

C C C C H H Cl H H

H butanal 3,3 dichloropentanal Ketones or Alkanones Suffix = one Propanone (also known as acetone) Butanone (also known as ethyl methyl ketone) Pentan-2-one

(note the number is necessary Because the C=O could be on carbon 2 or carbon 3) 77 Ketones H H O H H H C

C C C H H H H H H

H H H O H C C C C

C C H H H H H C

H H pentan-2-one hexan-2-one Carboxylic Acids R-COOH or R- HC2H3O2 CO2H This is a carbon to oxygen double bond with the

same carbon single-bonded to an OH group. Name as normal except give it the suffix -anoic Carboxylic Acids Suffix = oic Butanoic acid Note that the acid group (called a carboxyl) is always on an end carbon or carbon 1 80

Carboxylic Acids H HO H H H O C C

C C H H H O H H C

C C H H OH F Butanoic acid 3-Fluoropropanoic acid

Esters R-COO-R This is a carbon to oxygen double bond with a carbon to oxygen single bonded to another single bonded carbon Name by given secondary branch yl suffix and main branch -anoate suffix. Esters Esters

Suffix = oate Ethyl butanoate Butyl ethanoate There are two branches. The branch with the carbonyl gets the suffix 83 Esters Secondary Branch Main Branch

H H H H H O C C

C C C H H H H H O

C H H methyl pentanoate Methyl Pentanoate Esters H H H

O C C C H H H H C

H O O H H H H C C

C C H H H H O H

H H H H C C C C C

C H H H H H H H

Butyl propanoate Methyl hexanoate Amines R-NH2 Name the R group or groups with -yl endings Add the word amine Amines Suffix = amine Or prefix = amino

Propylamine or 1-aminopropane 2-propylamine or 2-aminopropane 2-methyl-2-propylamine or 2-methyl -2- aminopropane 87 Amines H H H C H

Methyl amine N H H H H C N H

C H H H Dimethyl amine Amides Suffix = amide butanamide Note that the amide group is always on an

end carbon or carbon 1 89 Summary Cl R R R OH R

O Halide Alcohol Ether O O O C H

R C OH R C Carboxylic Acid R Ketone Aldehyde O R

O C Ester R R R NH2 Amine Summary Alkanes Alkenes

Alkynes Halides Alcohols Ethers Aldehydes Ketones Carboxylic Acids Esters Amines - -ane = -ene -yne R-X -o R-OH -ol R-O-R

-yl ether R-COH -al R-CO-R -one R-COOH -anoic acid R-COO-R -yl -anoate R-NH2 -yl amine Can You Do This? YES! It takes: Memorization Practice Practice Practice Practice And, oh yes Practice!

Classifications Primary Secondary and tertiary Halogenoalkanes , Alcohols and Amines Learning Objectives Distinguish between primary secondary and tertiary Alcohols. Distinguish between primary secondary and tertiary halogenoalkanes. Distinguish between primary secondary and tertiary Amines. Classifications of Alcohol Learning Objectives Distinguish between primary secondary

and tertiary Alcohols Primary, secondary and Tertiary carbon Primary = a carbon attached to only ONE other carbon Secondary = a carbon attached to only TWO other carbons Tertiary = a carbon attached to THREE other carbons Primary Alcohols A primary alcohol has only one carbon atom attached Secondary Alcohols A secondary alcohol has 2 carbon chains attached to the group on which the OH resides Tertiary Alcohols

Is cholesterol a primary, secondary or tertiary alcohol? Secondary Classification of Halogenoalkanes Learning Objectives Distinguish between primary secondary and tertiary Halogenoalkanes Primary Halogenoalkane In a primary (1) halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group. Some examples of primary halogenoalkanes

include: Secondary halogenoalkanes In a secondary (2) halogenoalkane, the carbon with the halogen attached is joined directly to two other alkyl groups, which may be the same or different. Examples: Tertiary halogenoalkanes In a tertiary (3) halogenoalkane, the carbon atom holding the halogen is attached directly to three alkyl groups, which may be any combination of same or different. Examples:

Practice Classification of Amines Learning Objectives Distinguish between primary secondary and tertiary Amines Primary amines In primary amines, only one of the hydrogen atoms in the ammonia molecule has been replaced. That means that the formula of the primary amine will be RNH 2 where "R" is an alkyl group. Examples include:

Secondary amines In a secondary amine, two of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. At this level, you are only likely to come across simple ones where both of the hydrocarbon groups are alkyl groups and both are the same. For example: Tertiary amines In a tertiary amine, all of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. Again, you are only likely to come across simple ones where all three of the hydrocarbon groups are alkyl groups and all three are the same. The naming is similar to secondary amines. For example:

Practice Structure of Benzene Learning outcome Benzene is an aromatic, unsaturated hydrocarbon represented by . Use physical and chemical evidence to discuss the structure of benzene. The Kekul structure for benzene, C6H6 Kekul was the first to suggest a sensible structure for benzene. The carbons are arranged

in a hexagon, and he suggested alternating double and single bonds between them. Each carbon atom has a hydrogen attached to it. Kekuledrea m This diagram is often simplified by leaving out all the carbon and hydrogen atoms!

Problems with the Kekul structure Problems with the chemistry Because of the three double bonds, you might expect benzene to have reactions like ethene. Ethene undergoes addition reactions in which one of the two bonds joining the carbon atoms breaks, and the electrons are used to bond with additional atoms. Benzene rarely does this. Instead, it usually undergoes substitution reactions in which one of the hydrogen atoms is replaced by something new Problems with the Kekul structure Problems with the shape Benzene is a planar molecule (all the atoms lie in

one plane), and that would also be true of the Kekul structure. The problem is that C-C single and double bonds are different lengths. C-C 0.154 nm C=C 0.134 nm That would mean that the hexagon would be irregular if it had the Kekul structure, with alternating shorter and longer sides. In real benzene all the bonds are exactly the same - intermediate in length between C-C and C=C at 0.139 nm. Real benzene is a perfectly regular hexagon Problems with the Kekul structure Problems with the

stability of benzene Real benzene is a lot more stable than the Kekul structure would give it credit for. Every time you do a thermochemistry calculation based on the Kekul structure, you get an answer which is wrong by about 150 kJ mol-1. This is most easily shown using enthalpy changes of hydrogenation. Molecular Structure of benzene Each of the six carbon atoms is sp2 hybridized

forming 3 sigma bonds with angles of 120, making a planar shape. This leaves one unhybridized p electron on each carbon atom with its dumb-bell shape perpendicular to the plane of the ring. The p orbitals effectively overlap in both directions spreading themselves out evenly to be shared by all 6 carbon atoms. This forms a delocalized pi electron cloud in which electron density is concentrated in two donut-shaped rings above and below the plane of the ring. This very stable arrangement lowers the internal energy of the molecule.

Orbital Structure Video The symbol for benzene Although you will still come across the Kekul structure for benzene, for most purposes we use the structure on the right. The hexagon shows the ring of six carbon atoms, each of which has one hydrogen attached. The circle represents the delocalised electrons. It is essential that you include the circle. If you miss it out, you

are drawing cyclohexane and not benzene. Theory of Knowledge Kekule claimed that the inspiration for the cyclic structure of benzene came from a dream. What role to the less analytical ways of knowledge play in the acquisition of scientific knowledge? Citation http://www.chemguide.co.uk

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