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Full structure H HH H C H H C H H C C H C C H H C O H C C C H H H H H H H H H H H H C C C C H H H H C C C H H C H H H H C C C C H H H C H H H C H C H C H H C H H How do we simplify this? • we need a set of rules that is consistent • rules should be based on simple (even obvious) criteria • rules need to make it easier to see the important parts of the molecule There are three kinds of atoms • Carbon — C • Hydrogen — H • Heteroatoms — everything else in the periodic table Basis for structure-simplifying rules • Every organic compound has carbon – let’s omit the symbol for carbon • means that the reader will need to know that we don’t explicitly show carbon atoms any more H H H H H H H H H C C C C H H H C H C C H HC H H H H H C C C C HHH HC H H H H C H H HC H H C C H C C H C C H C H H H H C C C H O H C C H H H H H H H HHH H H is simplified to H H H H H H H H H H H O H H H H H H H H H H H H H H H H H H H H H H H H H H H Next… • Hydrogen is almost always present in an organic compound • Carbon-hydrogen bonds are usually unreactive, so they seldom participate in any reactions – let’s omit the hydrogen atoms bonded to carbon • the reader will now need to know that any hydrogen atom bonded to carbon will not show up in the structural formula as drawn. H H H HHH H H H H H H H H H H H H H O H H H H H H H H H H H H H H H H H H H H H H H H H H H is simplified to H O Going the other way: Rules for interpreting organic structures • Carbon is always present in every organic molecule – assume carbon is at each end of every bond unless another atom is explicitly specified. • means that there is a carbon atom at the end of every line H O C becomes C H O C C C C C C C C C C C C C C C C C C C C C C C C C Rules for interpreting organic structures (continued) • Carbon is always tetravalent — it always has four covalent bonds • Hydrogen atoms bonded to carbon atoms are usually omitted from the structure – any carbons with less than four explicitly specified bonds carry hydrogen atoms – there must be enough hydrogen atoms to make up all four bonds to carbon for every carbon atom in the molecule C C H O C C C C C C C C C C C C C C C C C C C C C C C C C becomes H HH H C H H C H H C C H C C H H C O H C C C H H H H H H H H H H H H C C C C H H H H C C C H H C H H H H C C C C H H H H C H H C H C H C H H C H H What is more visible in this representation? • The substructures of the molecule – 4 rings – a tail hanging off one end H O • the chemically reactive parts of the molecule – the —O—H group – the carbon-carbon double bond What advantages do we gain? • we get a better idea of the actual shape of the molecule • we get a better focus on the important parts of the molecule • the drawing is much less busy and simpler to interpret — we can see the functional groups easily Functional Groups • Most of an organic compound does not react • Carbon-carbon and carbon-hydrogen single bonds almost never react • Carbon-carbon multiple bonds react with many reagents • Heteroatoms represent sites of reactivity in an organic molecule. • The reactive part of a molecule is called the FUNCTIONAL GROUP – multiple bonds are functional groups – heteroatoms are functional groups – C-C and C-H single bonds are not functional groups So what does this molecule really look like? Three different kinds of representation of the “real” cholesterol molecule Make-up of simple organic compounds • The compound consists of two parts R OH alcohols – the functional group • site of reactivity • “where the action is” R O C H aldehydes R C N nitriles R O C R R C C R alkynes R ketones O C OR esters – “Vegas Strip” – the “rest of the molecule” • designated by “R” R R C C R R R alkenes aromatic rings R N R amines