Chapter 21

Chapter 21

Chapter 21 Fuels and Heats of Reaction Organic chemistry Organic chemistry is defined as the study of the compounds of carbon. A hydrocarbon is a compounds of carbon and hydrogen only. Types of hydrocarbon. Aliphatic- have molecules in chains or rings of carbon atoms. Aromatic - hydrocarbons with a Benzene ring of 6 carbon atoms, where the bonds are intermediate between single and double bonds. Aliphatic hydrocarbons. A homologous series is a group of compounds with similar chemical properties due to having the same functional group. They have a gradual variation in physical properties and they differ from each other by CH2. A functional group is a group of atoms within the molecule

which, due to its structure, gives the molecule its characteristics.(-OH functional group gives alcohols their characteristics) The 3 main classes of Hydrocarbons are Alkanes, Alkenes and Alkynes. Alkanes Formerly known as the paraffins (from the Latin meaning lacking affinity) the alkanes are a group of hydrocarbons which conform to the general formula CnH2n+2, where n is greater than or equal to 1. They are saturated compounds. They consist of carbon atoms joined by four single covalent bonds to either hydrogen or other carbon atoms. The first member of the group is methane (CH4), the second is ethane (C2H6), and the third is propane (C3H8), as illustrated in Fig. 3.2. By drawing their structural formulae we can see that each differs from the next by replacing a hydrogen with a CH3 group, i.e. an extra CH2 is inserted in the chain. ALKANES

General members of a homologous series general formula is CnH2n+2 - for non-cyclic alkanes saturated hydrocarbons - all carbon-carbon bonding is single bonds are spaced tetrahedrally about carbon atoms. Isomerism the first example of structural isomerism occurs with C4H10 BUTANE 2-METHYLPROPANE Structural isomers have the SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULA They possess different physical properties such as boiling point, melting point and density THE STRUCTURE OF ALKANES

In ALKANES, the four sp3 orbitals of carbon repel each other into a TETRAHEDRAL arrangement with bond angles of 109.5. Each sp3 orbital in carbon overlaps with the 1s orbital of a hydrogen atom to form a C-H bond. 109.5 Nomenclature of alkanes Naming straight-chain alkanes Naming of straight chain alkanes (alkanes that do not branch) is a straightforward process. To give an alkane a name, a prefix indicating

the number of carbons in the molecule is added to the suffix ane, identifying both the kind of molecule (an alkane) and how many carbons the molecule has (the prefix). The name pentane, for example, tells you that the molecule is an alkane (thus the ane ending) and that it has five carbons (pent indicates five). Prefixes for alkanes that have 1-4 carbons are rooted historically. These are methane, ethane, propane, and butane, respectively. On the other hand, for 5 carbons and up a prefix derived from greek is given. (An easy way to remember the first four names is the anagram, standing for methane, ethane, propane, butane). Learning the prefixes for up to twelve carbons is a good idea, and they are listed in the figure below. Molecular Formula Structural Formula IUPAC Name CH4 CH4

Methane C 2 H6 CH3-CH3 Ethane C 3 H8 CH3-CH2-CH3 Propane C4H10 CH3-(CH2)2-CH3 Butane

C5H12 CH3-(CH2)3-CH3 Pentane C6H14 CH3-(CH2)4-CH3 Hexane C7H16 CH3-(CH2)5-CH3 Heptane C8H18 CH3-(CH2)6-CH3

Octane C9H20 CH3-(CH2)7-CH3 Nonane C10H22 CH3-(CH2)8-CH3 Decane Naming branched alkanes There are several rules that you must follow to give the alkane the correct name. 1. Find the longest chain of carbons in the molecule. The number of carbons in the longest chain becomes the parent name (refer to the above table)

2. After finding the parent chain, you number the parent chain starting with the end nearest the first substituent (a substituent is any fragment that juts off the main chain). 3. Next, determine the names of all substituents. Substituents are named as if the piece were a separate molecule, except that the suffix of yl is used rather than ane. Thus, a two-carbon substituent would be an ethyl substituent (not an ethane substituent). 4. Put the substituents in alphabetical order (ie. ethyl before methyl) in front of the parent name. 5. Next, identify the positions of all substituents in the name by placing the carbon number where the substituent attaches to the parent chain in front of it. For example, 2-methylheptane indicates that a methyl substituent is attached to the number 2 carbon Mary eats peanut butter PHYSICAL PROPERTIES OF ALKANES Boiling point

increases as they get more carbon atoms in their formula more atoms = greater intermolecular Van der Waals forces greater intermolecular force = more energy to separate the molecules greater energy required = higher boiling point CH4 (-161C) C2H6 (-88C) C3H8 (-42C) C4H10 (-0.5C) difference gets less - mass increases by a smaller percentage straight chains molecules have greater interaction than branched The greater the branching, the lower the boiling point Melting point general increase with molecular mass the trend is not as regular as that for boiling point.

Solubilityalkanes are non-polar so are immiscible with water they are soluble in most organic solvents. CHEMICAL PROPERTIES OF ALKANES Introduction - fairly unreactive; (old family name, paraffin, meant little reactivity) - have relatively strong, almost NON-POLAR, SINGLE covalent bonds - they have no real sites that will encourage substances to attack them Combustion - make useful fuels - especially the lower members of the series - react with oxygen in an exothermic reaction BUT Handy tip complete combustion

CH4(g) + 2O2(g) incomplete combustion CH4(g) + 1O2(g) > CO2(g) + 2H2O(l) >

CO(g) 2H2O(l) + the greater the number of carbon atoms, the more energy produced the greater the amount of oxygen needed for complete combustion. When balancing equations involving complete combustion, remember... every carbon in the original hydrocarbon gives one carbon dioxide and every two hydrogen atoms gives a water molecule. Put the numbers into the equation, count up the Os and Hs on the RHS of the equation then balance the oxygen molecules on the LHS. POLLUTION Processes involving combustion give rise to a variety of pollutants... power stations internal combustion engines

Removal SO2 CO and NOx SO2 emissions produce acid rain CO, NOx and unburnt hydrocarbons react effluent gases with a suitable compound (e.g. CaO) pass exhaust gases through a catalytic converter Catalytic converters In the catalytic converter ... CO is converted to CO2 NOx are converted to N2 Unburnt hydrocarbons are converted to CO2 and H2O e.g. 2NO + 2CO

> N2 + 2CO2 catalysts are made of finely divided rare metals Rh, Pd, Pt leaded petrol must not pass through the catalyst as the lead deposits on the catalysts surface and poisons it, thus blocking sites for reactions to take place. Alkenes Alkenes Ethene C2H4 Propene C3H6 But-1-ene C4H8 But-2-ene C4H8

General Formula CnH2n Alkenes Alkenes are unsaturated hydrocarbons, as they contain a carbon-carbon double bond Ethene C 2 H4 Propene C 3 H6 But-1-ene C 4 H8

But-2-ene C 4 H8 Alkenes Alkene molecules are planar, e.g. ethene Physical properties Physical state: Gases Insoluble in water Soluble in non-polar solvents such as cyclohexane Uses Used to make plastics, e.g. ethene is used to make polythene Ethene is used to make ethanol for industrial use CRACKING

Involves the breaking of C-C bonds in alkanes Converts heavy fractions into higher value products THERMAL CATALYTIC proceeds via a free radical mechanism proceeds via a carbocation (carbonium ion) mechanism CATALYTIC SLIGHT PRESSURE HIGH TEMPERATURE ... 450C ZEOLITE CATALYST CARBOCATION (IONIC) MECHANISM HETEROLYTIC FISSION PRODUCES BRANCHED AND CYCLIC ALKANES, AROMATIC HYDROCARBONS USED FOR MOTOR FUELS ZEOLITES are crystalline aluminosilicates; clay like substances CRACKING Involves the breaking of C-C bonds in alkanes Converts heavy fractions into higher value products

THERMAL CATALYTIC proceeds via a free radical mechanism proceeds via a carbocation (carbonium ion) mechanism THERMAL HIGH PRESSURE ... 7000 kPa HIGH TEMPERATURE ... 400C to 900C FREE RADICAL MECHANISM HOMOLYTIC FISSION PRODUCES MOSTLY ALKENES ... e.g. ETHENE for making polymers and ethanol PRODUCES HYDROGEN ... used in the Haber Process and in margarine manufacture Bonds can be broken anywhere in the molecule by C-C bond fission or C-H bond fission Petrol Petrol is formed by the fractional distillation of crude oil. Some of the different fractions formed are: Petroleum Gas - Mercaptans added for smell. Petrol- light gasoline

Naphta - Petrochemical Industry Kerosene - Aviation Fuel. Diesel. Lubricating Oil. Octane Number Knocking - early explosion due to petrol-air mixture. The petrol explodes as it is compressed instead of being caused by a spark. (Auto-ignition). Octane Number - Measure of the tendency of fuels to resist knocking. 2, 2-4 tri-methyl pentane (iso-octane) has an octane number of 100. Heptane is not efficient and has an octane number of 0. The shorter the alkane the higher the octane number. The more branched the chain the higher the octane number. Cyclic compounds have a higher octane number than straight chain compounds. Making Petrol Knocking - early explosion due to petrol-air mixture. The petrol explodes as it is compressed instead of being caused by a spark. (Auto-ignition). Tetra-ethyl lead -Reduces knocking. However it caused health problems and is poisoness.

4 ways to increase octane number. 1. Isomerisation. Branching caused by alkanes heated in the presence of a suitable catalyst. 2. Catalytic Cracking. Long chained hydrocarbons broken down into short chain molecules for which there is great demand. Large alkanes form alkanes and alkenes. 3. Reforming (DeHydrocyclisation.) Reforming involves the use of catalysts to form ring compounds.-Hydrogen given off. 4. Adding Oxygenates. Three oxygen containing molecules, methanol, ethanol, and MTBE are added to petrol to increase its octane number. MTBE stands for methyl tertiary butyl ether. (2-methoxy-2-methylpropane) KNOCKHARDY PUBLISHING ORGANIC CHEMISTRY INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may

be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.argonet.co.uk/users/hoptonj/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard CONTENTS CONTENTS ORGANIC CHEMISTRY Organic chemistry is the study of carbon compounds. It is such a complex branch of chemistry because...

CARBON ATOMS FORM STRONG COVALENT BONDS TO EACH OTHER THE CARBON-CARBON BONDS CAN BE SINGLE, DOUBLE OR TRIPLE CARBON ATOMS CAN BE ARRANGED IN STRAIGHT CHAINS BRANCHED CHAINS and RINGS OTHER ATOMS/GROUPS OF ATOMS CAN BE PLACED ON THE CARBON ATOMS GROUPS CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON SKELETON CONTENTS CONTENTS SPECIAL NATURE OF CARBON - CATENATION CATENATION is the ability to form bonds between atoms of the same element. Carbon forms chains and rings, with single, double and triple covalent bonds, because it is able to FORM STRONG COVALENT BONDS WITH OTHER CARBON ATOMS

Carbon forms a vast number of carbon compounds because of the strength of the C-C covalent bond. Other Group IV elements can do it but their chemistry is limited due to the weaker bond strength. BOND ATOMIC RADIUS BOND ENTHALPY C-C 0.077 nm +348 kJmol-1 Si-Si 0.117 nm +176 kJmol-1

The larger the atoms, the weaker the bond. Shielding due to filled inner orbitals and greater distance from the nucleus means that the shared electron pair is held less strongly. CONTENTS CONTENTS THE SPECIAL NATURE OF CARBON CHAINS AND RINGS CARBON ATOMS CAN BE ARRANGED IN STRAIGHT CHAINS BRANCHED CHAINS and RINGS You can also get a combination of rings and chains CONTENTS

CONTENTS THE SPECIAL NATURE OF CARBON MULTIPLE BONDING AND SUBSTITUENTS CARBON-CARBON COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE CONTENTS CONTENTS THE SPECIAL NATURE OF CARBON MULTIPLE BONDING AND SUBSTITUENTS CARBON-CARBON COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE DIFFERENT ATOMS / GROUPS OF ATOMS CAN BE PLACED ON THE CARBONS The basic atom is HYDROGEN but groups containing OXYGEN, NITROGEN, HALOGENS and SULPHUR are very common. CARBON SKELETON

FUNCTIONAL GROUP CARBON SKELETON FUNCTIONAL GROUP The chemistry of an organic compound is determined by its FUNCTIONAL GROUP CONTENTS CONTENTS THE SPECIAL NATURE OF CARBON MULTIPLE BONDING AND SUBSTITUENTS ATOMS/GROUPS CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON SKELETON THE C=C DOUBLE BOND IS IN A DIFFERENT POSITION PENT-1-ENE PENT-2-ENE

THE CHLORINE ATOM IS IN A DIFFERENT POSITION 1-CHLOROBUTANE 2-CHLOROBUTANE CONTENTS CONTENTS TYPES OF FORMULAE - 1 MOLECULAR FORMULA C4H10 THE EXAMPLE BEING The exact number of atoms of each element present in the molecule EMPIRICAL FORMULA

USED IS... BUTANE C2H5 The simplest whole number ratio of atoms in the molecule STRUCTURAL FORMULA CH3CH2CH2CH3 The minimal detail using conventional groups, for an unambiguous structure DISPLAYED FORMULA Shows both the relative placing of atoms and the number of bonds between them

CH3CH(CH3)CH3 there are two possible structures H H H H H C C C C

H H H H H H H H H C

C C H H H C H H CONTENTS CONTENTS H TYPES OF FORMULAE - 2 SKELETAL FORMULA A skeletal formula is used to show a simplified organic formula by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups CH2 CH2

CH2 CH2 CH2 for CH2 CYCLOHEXANE THALIDOMIDE CONTENTS CONTENTS TYPES OF FORMULAE - 2 SKELETAL FORMULA A skeletal formula is used to show a simplified organic formula by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups CH2

CH2 CH2 CH2 CH2 for CH2 CYCLOHEXANE THALIDOMIDE GENERAL FORMULA Represents any member of a homologous series for alkanes it is... possible formulae...

CnH2n+2 CH4, C2H6 .... C99H200 The formula does not apply to cyclic compounds such as cyclohexane is C6H12 - by joining the atoms in a ring you need fewer Hs CONTENTS CONTENTS HOMOLOGOUS SERIES A series of compounds of similar structure in which each member differs from the next by a common repeating unit, CH2. Series members are called homologues and... all share the same general formula. formula of a homologue differs from its neighbour by CH2. (e.g. CH4, C2H6, ... etc ) contain the same functional group have similar chemical properties. show a gradual change in physical properties as molar mass increases. can usually be prepared by similar methods. ALCOHOLS - FIRST THREE MEMBERS OF THE SERIES

CH3OH METHANOL C2H5OH ETHANOL CONTENTS CONTENTS C3H7OH PROPAN-1-OL FUNCTIONAL GROUPS Organic chemistry is a vast subject so it is easier to split it into small sections for study. This is done by studying compounds which behave in a similar way because they have a particular atom, or group of atoms, FUNCTIONAL GROUP, in their structure. Functional groups can consist of one atom, a group of atoms or multiple bonds between carbon atoms. Each functional group has its own distinctive properties which means that the properties of a compound are governed by the functional group(s) in it.

H H H H H H H H H H H C C C C C H C C C C C NH2 H H H H H H H H H H Carbon skeleton OH Functional Group = AMINE

CONTENTS CONTENTS Carbon skeleton Functional Group = ALCOHOL COMMON FUNCTIONAL GROUPS GROUP ENDING ALKANE - ane ALKENE ALKYNE

GENERAL FORMULA RH EXAMPLE C2H6 ethane - ene C2H4 ethene - yne C2H2 ethyne HALOALKANE

halo - RX C2H5Cl chloroethane ALCOHOL - ol ROH C2H5OH ethanol -al

RCHO CH3CHO ethanal KETONE - one RCOR CH3COCH3 propanone CARBOXYLIC ACID - oic acid RCOOH

CH3COOH ethanoic acid ACYL CHLORIDE - oyl chloride RCOCl CH3COCl ethanoyl chloride AMIDE - amide RCONH2

CH3CONH2 ethanamide ESTER - yl - oate RCOOR CH3COOCH3 methyl ethanoate NITRILE - nitrile RCN CH3CN

ethanenitrile AMINE - amine RNH2 CH3NH2 methylamine NITRO nitro- RNO2 CH3NO2

nitromethane ALDEHYDE SULPHONIC ACID - sulphonic acid RSO3H C6H5SO3H benzene sulphonic acid ETHER - oxy - ane ROR CONTENTS

C2H5OC2H5 ethoxyethane CONTENTS COMMON FUNCTIONAL GROUPS ALKANE CARBOXYLIC ACID ALKENE ALKYNE ESTER HALOALKANE ACYL CHLORIDE AMINE NITRILE

AMIDE ALCOHOL ETHER NITRO ALDEHYDE SULPHONIC ACID KETONE CONTENTS CONTENTS HOW MANY STRUCTURES? Draw legitimate structures for each molecular formula and classify each one according to the functional group present. Not all the structures represent stable compounds. carbon atoms have oxygen atoms

nitrogen atoms hydrogen halogen atoms 4 covalent bonds surrounding them 2 3 1 1 C2H6 ONE C3H9Br TWO C4H8 FIVE - 3 with C=C and 2 ring compounds with all C-Cs

C2H6O TWO - 1 with C-O-C and 1 with C-O-H C3H6O SIX - 2 with C=O, 2 with C=C and 2 with rings C2H7N TWO C2H4O2 SEVERAL - Only 2 are stable C2H3N TWO

CONTENTS CONTENTS HOW MANY STRUCTURES? Draw legitimate structures for each molecular formula and classify each one according to the functional group present. Not all the structures represent stable compounds. carbon atoms have oxygen atoms nitrogen atoms hydrogen halogen atoms 4 covalent bonds surrounding them 2 3 1 1 C2H6 ONE

C3H9Br TWO C4H8 FIVE - 3 with C=C and 2 ring compounds with all C-Cs C2H6O TWO - 1 with C-O-C and 1 with C-O-H C3H6O SIX - 2 with C=O, 2 with C=C and 2 with rings C2H7N TWO

C2H4O2 SEVERAL - Only 2 are stable C2H3N TWO CONTENTS CONTENTS NOMENCLATURE Ideally a naming system should tell you everything about a structure without ambiguity. There are two types of naming system commonly found in organic chemistry; Trivial : Systematic : based on some property or historical aspect; the name tells you little about the structure based on an agreed set of rules (I.U.P.A.C); exact structure can be found from the name (and vice-versa).

trivial name paraffin olefin fatty acid trivial name methane butane acetic acid HOMOLOGOUS SERIES systematic name example(s) alkane methane, butane alkene ethene, butene alkanoic (carboxylic) acid ethanoic acid

INDIVIDUAL COMPOUNDS derivation systematic name methu = wine (Gk.) methane (CH4) butyrum = butter (Lat.) butane (C4H10) acetum = vinegar (Lat.) ethanoic acid (CH3COOH) CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE A systematic name has two main parts. STEM number of carbon atoms in longest chain bearing the functional group + a prefix showing the position and identity of any side-chain substituents. Apart from the first four, which have trivial names, the number of carbons atoms is indicated by a

prefix derived from the Greek numbering system. The list of alkanes demonstrate the use of prefixes. The ending -ane is the same as they are all alkanes. Prefix methethpropbutpenthexheptoctnondec- C atoms 1 2 3 4 5 6 7 8 9 10

Alkane methane ethane propane butane pentane hexane heptane octane nonane decane Working out which is the longest chain can pose a problem with larger molecules. CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE How long is a chain? Because organic molecules are three dimensional and paper is two dimensional it can confusing when comparing molecules. This is because...

1. It is too complicated to draw molecules with the correct bond angles 2. Single covalent bonds are free to rotate All the following written structures are of the same molecule - PENTANE C5H12 CH3 CH3 CH2 CH2 CH2 CH3 CH2 CH2 CH2 CH3 CH3 CH2 CH2 CH2 CH3 CH2 CH3 CH3 CH2 CH2 A simple way to check is to run a finger along the chain and see how many carbon atoms can be covered without reversing direction or taking the finger off the page.

In all the above there are... FIVE CARBON ATOMS IN A LINE. CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE How long is the longest chain? Look at the structures and work out how many carbon atoms are in the longest chain. CH3 THE ANSWERS ARE ON THE NEXT SLIDE CH2 CH3 CH CH2 CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH3 CH3 CH2 CH3 CH2 CH CH CH3 CONTENTS

CONTENTS I.U.P.A.C. NOMENCLATURE How long is the longest chain? Look at the structures and work out how many carbon atoms are in the longest chain. CH3 LONGEST CHAIN = 5 CH2 CH3 CH CH2 CH3 CH3 LONGEST CHAIN = 6 CH3 CH2 CH2 CH2 CH CH3 CH3 CH3 CH2 LONGEST CHAIN = 6

CH3 CH2 CH CH CH3 CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE A systematic name has two main parts. SUFFIX An ending that tells you which functional group is present See if any functional groups are present. Add relevant ending to the basic stem. In many cases the position of the functional group must be given to avoid any ambiguity 1-CHLOROBUTANE SUBSTITUENTS Functional group Suffix ALKANE

ALKENE ALKYNE ALCOHOL ALDEHYDE KETONE ACID - ANE - ENE - YNE - OL - AL - ONE - OIC ACID 2-CHLOROBUTANE Many compounds have substituents (additional atoms, or groups) attached to the chain. Their position is numbered. CONTENTS

CONTENTS I.U.P.A.C. NOMENCLATURE SIDE-CHAIN carbon based substituents are named before the chain name. they have the prefix -yl added to the basic stem (e.g. CH3 is methyl). Alkyl radicals methyl CH3 - CH3 ethyl CH3- CH2- C2H5

propyl CH3- CH2- CH2- C3H7 Number the principal chain from one end to give the lowest numbers. Side-chain names appear in alphabetical order butyl, ethyl, methyl, propyl Each side-chain is given its own number. If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa Numbers are separated from names by a HYPHEN e.g. Numbers are separated from numbers by a COMMA e.g. 2,3-dimethylbutane

CONTENTS CONTENTS 2-methylheptane I.U.P.A.C. NOMENCLATURE SIDE-CHAIN carbon based substituents are named before the chain name. they have the prefix -yl added to the basic stem (e.g. CH3 is methyl). Alkyl radicals methyl CH3 - CH3 ethyl CH3- CH2-

C2H5 propyl CH3- CH2- CH2- C3H7 Number the principal chain from one end to give the lowest numbers. Side-chain names appear in alphabetical order butyl, ethyl, methyl, propyl Each side-chain is given its own number. If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa Numbers are separated from names by a HYPHEN e.g. Numbers are separated from numbers by a COMMA

e.g. 2,3-dimethylbutane Example longest chain 8 (it is an octane) 3,4,6 are the numbers NOT 3,5,6 order is ethyl, methyl, propyl 3-ethyl-5-methyl-4-propyloctane 2-methylheptane CH3 CH3 CH3 CH2 CH2 CH CH2 CH3 CH2 CH2 CH CH

CONTENTS CONTENTS CH2 CH3 I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes THE ANSWERS ARE ON THE NEXT SLIDE CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH3 CH3 CH2 CH3 CH2 CH CH CH3 CONTENTS

CONTENTS I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH3 CH3 CH2 CH3 CH2 CH CH CH3 CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes Longest chain = 5 so it is a pentane

CH3 A CH3, methyl, group is attached to the third carbon from one end... CH2 CH3 CH CH2 CH3 3-methylpentane CH3 CH3 CH2 CH2 CH2 CH CH3 CH3 CH3 CH2 CH3 CH2 CH CH CH3 CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes

Longest chain = 5 so it is a pentane CH3 A CH3, methyl, group is attached to the third carbon from one end... CH2 CH3 CH CH2 CH3 3-methylpentane CH3 CH3 CH2 CH2 CH2 CH CH3 Longest chain = 6 so it is a hexane A CH3, methyl, group is attached to the second carbon from one end... 2-methylhexane CH3

CH3 CH2 CH3 CH2 CH CH CH3 CONTENTS CONTENTS I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes Longest chain = 5 so it is a pentane CH3 A CH3, methyl, group is attached to the third carbon from one end... CH2 CH3 CH CH2 CH3 3-methylpentane CH3 CH3 CH2 CH2 CH2 CH CH3

Longest chain = 6 so it is a hexane A CH3, methyl, group is attached to the second carbon from one end... 2-methylhexane CH3 CH3 CH2 CH3 CH2 CH CH CH3 Longest chain = 6 so it is a hexane CH3, methyl, groups are attached to the third and fourth carbon atoms (whichever end you count from). 3,4-dimethylhexane CONTENTS CONTENTS NAMING ALKENES Length

In alkenes the principal chain is not always the longest chain It must contain the double bond the name ends in -ENE Position Count from one end as with alkanes. Indicated by the lower numbered carbon atom on one end of the C=C bond 5 4 3 2 1 CH3CH2CH=CHCH3 Side-chain

is pent-2-ene (NOT pent-3-ene) Similar to alkanes position is based on the number allocated to the double bond 1 2 3 4 1 2 3 4

CH2 = CH(CH3)CH2CH3 CH2 = CHCH(CH3)CH3 2-methylbut-1-ene 3-methylbut-1-ene CONTENTS CONTENTS WHICH COMPOUND IS IT? Elucidation of the structures of organic compounds - a brief summary Organic chemistry is so vast that the identification of a compound can be involved. The characterisation takes place in a series of stages (see below). Relatively large amounts of substance were required to elucidate the structure but, with modern technology and the use of electronic instrumentation, very small amounts are now required. Elemental composition One assumes that organic compounds contain carbon and hydrogen but it can be

proved by letting the compound undergo combustion. Carbon is converted to carbon dioxide and hydrogen is converted to water. Percentage composition by mass Found by dividing the mass of an element present by the mass of the compound present, then multiplying by 100. Elemental mass of C and H can be found by allowing the substance to undergo complete combustion. From this one can find... mass of carbon mass of hydrogen = = 12/44 of the mass of CO2 produced 2/18 of the mass of H2O produced CONTENTS CONTENTS INVESTIGATING MOLECULES Empirical formula The simplest ratio of elements present in the substance. It is calculated by dividing the mass or percentage mass of each element by its molar mass and finding the simplest

ratio between the answers. Empirical formula is converted to the molecular formula using molecular mass. CONTENTS CONTENTS INVESTIGATING MOLECULES Empirical formula The simplest ratio of elements present in the substance. It is calculated by dividing the mass or percentage mass of each element by its molar mass and finding the simplest ratio between the answers. Empirical formula is converted to the molecular formula using molecular mass. Molecular mass Traditionally found out using a variety of techniques such as ... volumetric analysis or molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass spectrometry is now used. The m/z value of the molecular ion and gives the molecular mass. The fragmentation pattern gives information about the compound. CONTENTS CONTENTS

INVESTIGATING MOLECULES Empirical formula The simplest ratio of elements present in the substance. It is calculated by dividing the mass or percentage mass of each element by its molar mass and finding the simplest ratio between the answers. Empirical formula is converted to the molecular formula using molecular mass. Molecular mass Traditionally found out using a variety of techniques such as ... volumetric analysis or molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass spectrometry is now used. The m/z value of the molecular ion and gives the molecular mass. The fragmentation pattern gives information about the compound. Molecular formula The molecular formula is an exact multiple of the empirical formula. Comparing the molecular mass with the empirical mass allows one to find the true formula. e.g. if the empirical formula is CH (relative mass = 13) and the molecular mass is 78 the molecular formula will be 78/13 or 6 times the empirical formula i.e. C6H6 . CONTENTS CONTENTS INVESTIGATING MOLECULES

Empirical formula The simplest ratio of elements present in the substance. It is calculated by dividing the mass or percentage mass of each element by its molar mass and finding the simplest ratio between the answers. Empirical formula is converted to the molecular formula using molecular mass. Molecular mass Traditionally found out using a variety of techniques such as ... volumetric analysis or molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass spectrometry is now used. The m/z value of the molecular ion and gives the molecular mass. The fragmentation pattern gives information about the compound. Molecular formula The molecular formula is an exact multiple of the empirical formula. Comparing the molecular mass with the empirical mass allows one to find the true formula. e.g. if the empirical formula is CH (relative mass = 13) and the molecular mass is 78 the molecular formula will be 78/13 or 6 times the empirical formula i.e. C6H6 . Structural formula Because of the complexity of organic molecules, there can be more than one structure for a given molecular formula. To work out the structure, different tests are carried out. CONTENTS CONTENTS

INVESTIGATING MOLECULES Empirical formula The simplest ratio of elements present in the substance. It is calculated by dividing the mass or percentage mass of each element by its molar mass and finding the simplest ratio between the answers. Empirical formula is converted to the molecular formula using molecular mass. Molecular mass Traditionally found out using a variety of techniques such as ... volumetric analysis or molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass spectrometry is now used. The m/z value of the molecular ion and gives the molecular mass. The fragmentation pattern gives information about the compound. Molecular formula The molecular formula is an exact multiple of the empirical formula. Comparing the molecular mass with the empirical mass allows one to find the true formula. e.g. if the empirical formula is CH (relative mass = 13) and the molecular mass is 78 the molecular formula will be 78/13 or 6 times the empirical formula i.e. C6H6 . Structural formula Because of the complexity of organic molecules, there can be more than one structure for a given molecular formula. To work out the structure, different tests are carried out. CONTENTS CONTENTS

INVESTIGATING MOLECULES Chemical Chemical reactions can identify the functional group(s) present. Spectroscopy IR detects bond types due to absorbance of i.r. radiation NMR gives information about the position and relative numbers of hydrogen atoms present in a molecule By comparison of IR or NMR spectra and mass spectrometry

Confirmation CONTENTS CONTENTS REVISION CHECK What should you be able to do? Recall and explain the reasons for the large number of carbon based compounds Be able to write out possible structures for a given molecular formula Recognize the presence of a particular functional group in a structure Know the IUPAC rules for naming alkanes and alkenes Be able to name given alkanes and alkenes when given the structure Be able to write out the structure of an alkane or alkene when given its name Recall the methods used to characterise organic molecules CAN YOU DO ALL OF THESE? CONTENTS CONTENTS

YES NO You need to go over the relevant topic(s) again Click on the button to return to the menu CONTENTS CONTENTS WELL DONE! Try some past paper questions CONTENTS CONTENTS ORGANIC CHEMISTRY

AN INTRODUCTION TO THE END 2003 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

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