General Organic Chemistry PDF

AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY BONDING IN ORGANIC CHEMISTRY Carbon (C) is the basis for all organic chemistry. Being in Group 4, carbon has 4 valence (outer) electrons, so can form 4 covalent bonds with itself and other at...

AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY BONDING IN ORGANIC CHEMISTRY Carbon (C) is the basis for all organic chemistry. Being in Group 4, carbon has 4 valence (outer) electrons, so can form 4 covalent bonds with itself and other atoms. This gives it a unique ability to form a wide variety of complex molecules. C C Carbon most often forms 4 single Carbon can make double bonds with covalent bonds with 4 other atoms. some other atoms, including other This gives a tetrahedral shape carbon atoms. around the carbon atom (109.5o This gives a trigonal planar shape bond angle). around the carbon atom (120o bond Organic molecules where all carbon angle). atoms have 4 single covalent bonds Organic molecules that contain are termed “saturated” as no more carbon to carbon double bonds bonds can be made around the (C=C) are termed “unsaturated” as carbon atoms. it is possible for the C atoms that have double bonds still have the ability to form a new bond with other atoms. More on C=C double binds in the Alkenes section. In organic molecules, unless a carbon atom is bonded to another carbon atom, they are bonded to hydrogen (H) atoms. This is why they are often referred to as hydrocarbons. A wide variety of other atoms and groups can also bond to the carbon atoms in them molecule creating what are known as functional groups. These change both the physical and chemical properties of the organic molecule. In the main, these functional groups are made up of a combination of oxygen atoms, halogen atoms and / or nitrogen atoms. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY ORGANIC FORMULAE FORMULA TYPE DESCRIPTION Each functional group has it's own general formula that all molecules follow. e.g. Alkanes - CnH2n+2 General Formula This means that there are always twice as many H atoms as there are C atoms… plus 2. e.g. If an alkane molecule contains 6 C atoms, it will contain 14 H atoms. This is the formula that gives the actual number Molecular Formula of each type of atom in the molecule. e.g. C6H14 This shows all of the covalent beings between the atoms in the molecule and is the most detailed formula that we can use. Displayed Formula e.g. H H H H H H H C C C C C C H H H H H H H This is the “written” version of the displayed formula and lists each C atom in the chain one Structural Formula at a time along with the atoms that each is bonded to. e.g. CH3CH2CH2CH2CH2CH3 This shows the “skeleton" of the molecule. C and H atoms are not shown. Only functional groups. The C-C bonds in the main skeleton Skeletal Formula are represented by a series of lines. e.g. This gives the simplest ratio of the atoms in the Empirical Formula molecule. e.g. C6H14 can be simplified to C3H7 The General, Displayed, Structural and Skeletal formula for each functional group will be discussed further in each section. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY NOMENCLATURE A.K.A. naming molecules! The naming system for organic molecules is complex but logical. It follows a set of I.U.P.A.C. rules (International Union of Pure & Applied Chemistry). This provides a truly international language for all chemists to use. When naming molecules, the core of the name always revolves around the longest continuous carbon chain in the molecule. You need to learn the nomenclature for up to and including 6 carbon atoms in a continuous chain. Number of Carbons Displayed Formula Name in the Longest Chain 1 C meth____ (“meeth”) 2 C–C eth____ (“eeth”) 3 C–C–C prop____ (“prope”) 4 C–C–C–C but____ (“byoot") 5 C–C–C–C–C pent____ 6 C–C–C–C–C–C hex____ The longest continuous carbon chain is the first thing you should look for when naming a molecule. The type of functional group present on the molecule can change the ending of the name. This is why gaps _____ have been left in the table above. e.g. Alkanes are named methane, ethane, propane etc Nomenclature specific to functional groups is covered at the beginning of each section for that functional group. e.g. alkanes, alkenes, halogenoalkanes etc AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY STRAIGHT CHAIN ALKANES Alkanes are the simplest form of organic molecule in that they are saturated and only contain carbon and hydrogen. General Formula: CnH2n+2 Naming: End in ____ane e.g. H H H H H H C H H C C C C H H H H H H methane butane H H H H H H H H C C H H C C C C C H H H H H H H H ethane pentane H H H H H H H H H H C C C H H C C C C C C H H H H H H H H H H propane hexane The name relates directly to the number of carbon atoms in a single, continuous chain. If we want to refer to a specific carbon in the chain, we must use the numbering system, where each carbon is assigned a number. E.g. in hexane, from 1 to 6. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY THE NUMBERING SYSTEM Two VERY important numbering rules: 1. You can number them from right to left, or left to right 2. If you need to refer to a specific carbon in a name, you always use the lowest number (or combination of numbers) possible. This will dictate in which direction you count. e.g. in hexane If there is an atom or group other H H H H H H than an H atom bonded to one of the C atoms in the chain, when 1 2 3 4 5 6 H C C C C C C H we name it, we must use these 6 5 4 3 2 1 numbers to states where it is. H H H H H H We could say that the “X” here is on carbon number 2 or carbon number 5. H X H H H H H However, according to the rules, 1 2 3 4 5 6 we must always use the lowest H C C C C C C H 6 5 4 3 2 1 number possible. In that respect, it would be correct to say that it is H H H H H H in position 2. It would incorrect to say it is in position 5. If we need to refer to two groups, we must choose the system that gives us the lowest possible combination of numbers. H H H X H X H H 1 2 3 4 5 6 Here we would use the blue H C C C C C C H system as 2 & 3 are lower than 4 6 5 4 3 2 1 & 5. H H H H H H You must never mix the systems. In other words, stick to the red system or the blue system! AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY CYCLICAL MOLECULES Carbon chains can also be “cyclical”. In other words, one end can be joined to the other. All of these have the general formula CnH2n. e.g. skeletal formulae cyclopropane cyclobutane cyclopentane cyclohexane Each carbon atom in the ring is bonded to 2 H atoms, so they actually look like… H H The displayed formula for H C H these cyclical alkanes can get quite “busy”. C C This is why you will see H H them represented as a C C skeletal formula most of H H the time. H H Displayed formula for cyclopentane HINTS | TIPS | HACKS Cycloalkanes have the same general formula as alkenes (CnH2n) You will not be asked to name any cyclical structures using the numbering system. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY BRANCHED CHAIN MOLECULES Not all organic molecules are “straight chain” molecules. The ability of carbon to form up to 4 carbon-carbon bonds mean that many molecules are “branched”. In other words, they have “side chains”. e.g. H CH3 H H H “Main”, longest chain Side chain H C C C C C H H H H H H Carbon side chains like this are known as “alkyl” side chains. You will likely only come across: methyl side chains (-CH3) ethyl side chains (-C2H5) We could call the molecule above methylpentane, but this doesn’t tell us where on the longest chain the methyl group is. This is where we use our numbering system. Using the lowest possible carbon number on the longest chain, this would be called 2-methylpentane. How to Draw & Name Branched Chain Molecules AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY FUNCTIONAL GROUP OVERVIEW A functional group is a part of an organic molecule that changes both the physical and chemical properties of the molecule. In the main, these functional groups are made up of a combination of oxygen atoms, halogen atoms and / or nitrogen atoms. Each of these is known as a homologous series. These are groups of compounds that have the same general formula and functional group. Each member of the series differs by “CH2”. Name Name Functional Group (Insert meth, eth, prop etc) Alkene C C _____ene e.g. fluoroethane Halogenoalkane C R X chloroethane bromoethane Alcohol C OH _____anol O *Aldehyde C _____anal H O _____anone *Ketone R C R O *Carboxylic Acid C _____anoic acid OH *Amine C NH2 _____ylamine *Nitrile C N _____anenitrile *You do not need to know details of these compounds just yet. Just recognise them and know that they are the products of reactions you will learn this year. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY ISOMERISM In organic chemistry, generally speaking, isomers are molecules that have the same molecular formula, but a different structure. In other words, the same type and number of atoms are present, but they are arranged in a different way. More specifically, there are different forms of isomerism that they can show. They are categorised as follows: Isomers Structural Isomers Stereoisomers These are molecules that have These are molecules that have the same molecular formula but the same structural formula but a different structural formula the atoms are arranged in different relative positions in space 1. Chain Isomers 1. E / Z Isomers Same molecular formula, but the These are specific to alkenes carbon chains have a different (molecules that contain a C=C). arrangement More on these in the alkenes section. 2. Position Isomers Same molecular formula, but the 2. Optical Isomers functional group is on a different These are covered in Year 13 position on the carbon chain 3. Functional Group Isomers Same molecular formula, but the atoms are rearranged to produce a different functional group. There are only a few of examples of these AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY CHAIN ISOMERS These have the same molecular formula, but the carbon chains have a different arrangement. To create chain isomers, you must “break” the carbon chain and reposition the carbons in a different order. The greater the number of C atoms, the greater the number of different chain isomers that are possible. e.g. molecular formula: C4H10 butane 2-methylpropane H H H H H CH3 H H C C C C H H C C C H H H H H H H H Structural Formula: CH3CH2CH2CH3 CH3CH(CH3)CH3 How to Deduce & Draw Chain Isomers AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY POSITION ISOMERS These have the same molecular formula, but the functional group is on a different position on the carbon chain. To create chain isomers, you just have to move the functional group to a different C atom in the chain. The greater the number of C atoms, the greater the number of different position isomers that are possible. e.g. molecular formula C4H9Cl 1-chlorobutane 2-chlorobutane Cl H H H H Cl H H H C C C C H H C C C C H H H H H H H H H Structural Formula: CH2ClCH2CH2CH3 CH3CHClCH2CH3 How to Deduce & Draw Position Isomers AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY FUNCTIONAL GROUP ISOMERS These have the same molecular formula, but the atoms are rearranged to produce a different functional group. There are a limited number of examples of these, and 2. & 3. involve functional groups that you will find in Year 13 s you don’t need to worry about them just yet! cyclobutane but-1-ene 1. Cycloalkanes & Alkenes H H H H H H e.g. C4H8 H C C H C C C C H H C C H H H H H H Cycloalkane alkene propanal propanone H H H O H 2. Aldehydes & Ketones O e.g. C3H8O H C C C H C C C H H H H H H aldehyde ketone propanoic acid methyl ethanoate H H H O H O 3. Carboxylic Acids & Esters H C C C H C O C C H e.g. C3H6O2 OH H H H H carboxylic acid ester AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.3.1 INTRO. TO ORGANIC CHEMISTRY REACTION MECHANISMS Reactions involving organic molecules can be explained using reactions mechanisms. These detail what happens to each atom / group in the molecule during the reaction. They show the dipoles present in the molecule and how the movement of electrons causes bonds to break and new bonds to be formed. Typically, these mechanisms show how one functional group is converted to another. KEY TERMS TERM DESCRIPTION An electron-rich species. Electron pair donator. Nucleophile Attracted to something positive e.g. NH3, Cl-, OH- An electron-deficient species. Electron pair acceptor. Electrophile Attracted to something negative e.g. H+ Addition An atom / group is added to the molecule Substitution An atom / group is exchanged for another in the molecule Elimination An atom / group is removed from the molecule Oxidation Addition of oxygen or removal of hydrogen Reduction Addition of hydrogen or removal of oxygen The name of each mechanism describes what is involved. e.g. electrophilic addition. How to Understand This means an electrophile is added to a molecule. Reaction Mechanisms Curly arrows are used to show the movement of a pair of electrons in mechanisms. These always result in the formation of a new covalent bond or the breaking of a covalent bond. AQA www.chemistrycoach.co.uk © scidekick ltd 2024