Organic Chemistry DP Chemistry
What is Organic Chemistry? • “Organic” is a term that is used in a variety of ways: • “from living things” • “chemical free” • “carbon-based” Organic Chemistry is the study of carbon-based compounds
C 12 6 Carbon • Carbon is in Group IV of the periodic table • Carbon has 4 valence electrons • Carbon can form 4 covalent bonds • Carbon can form single, double and triple bonds with a wide variety of elements forming nearly ten million known compounds 1s2 2s2 2p2
Carbon atom Hydrogen atoms Tetravalent Carbon Because carbon has four valence electrons, it forms four bonds with other elements to make up a full valence shell of 8. All valence electrons are involved in bonding. This bonding leads to tetrahedral shapes when all of the bonds involved are single bonds. Hydrocarbons are made up of carbon bonded to hydrogen, but many elements can and do take the place of hydrogen. Common elements that bond to carbon are N, O, S and the halogens (e.g. Cl, F). Methane CH4 Chlorine atoms Carbon atom Carbon tetrachloride CCl4
H H H H C C H H H H C C H H Carbon Bonding Molecular Formula Structural Formula Single bond - ethane C2H6 Double bond - ethene C2H4
H H C C Carbon Bonding Molecular Formula Structural Formula Triple bond – ethyne (acetylene) C2H2 Cyclic– benzene C6H6
Fractional Distillation Crude oil contains a mixture of hydrocarbons ranging from one carbon (C1) up to more than C24. Fractional distillation allows for these components or ‘fractions’ to be separated using a fractionating column. In this process, heat is applied to the bottom of the column and lighter compounds with lower boiling points rise to the top, while heavier compounds remain towards the bottom of the column. Source: http://www.bbc.co.uk/schools/gcsebitesize/chemistry/usefulproductsoil/oil_and_oilproductsrev5.shtml
Hydrocarbons Alkanes - hydrocarbons that contain only single bonds (all bonds and no bonds - saturated). The table to the right shows the alkane homologous series (a family of compounds that have the same general formula differing by CH2). Formula – CnH2n+2 Straight-chain alkanes – carbons joined together to form a single chain with no branching. Structural formulae Propane Butane Methane Ethane
CH2 CH2 CH3 CH CH3 CH2 CH2 CH3 CH CH2 CH2 CH CH2 CH Hydrocarbons Alkenes– hydrocarbons that contain one double bond between two carbon atoms. Formula – CnH2n Isomers – compounds that have the same molecular formula, but different structure. Alkenes have isomers because the double bond can be in a different location above C4. The location of the double bond is indicated by a numerical prefix counting from the shortest end. Condensed structural formulae 1-butene 1-pentene 2-pentene (NOT 3-pentene)
Hydrocarbons Alkynes – hydrocarbons that contain one triple bond between two carbon atoms. Formula – CnH2n-2 As with alkenes, a numerical prefix indicates the location of the triple bond.
Alkane b.p. trend As alkanes get larger in size, the intermolecular forces increase due to a greater amount of dispersion forces. The table below and graph to the right show the trend in boiling point for simple, straight-chain alkanes. The longer the chain, the greater the forces between molecules
Types of Formulae 4 Types: Empirical –this shows the ratio of elements in the compound Molecular – shows the actual number of atoms in a compound, but no information about how they are arranged Structural – shows the arrangement of elements and all of the bonds between them. Most appropriate Condensed Structural – omits some or all of the bonds and may show identical groups bracketed together.These are not acceptable when asked for a structural formula. e.g. CH3(CH2)4CH3 Condensed Structural Structural Formula Molecular
Structural Isomers Structural isomers are molecules that have the same molecular formula, but different structures. Butane Molecular formula: C4H10 Notice that changing the structure, changes some of the physical properties
Structural Isomers Pentane Notice again that changing the structure, changes some of the physical properties. What pattern do you notice with these isomers? M.p./b.p. decreases with more branching
Naming Hydrocarbons IUPAC IUPAC – The International Union of Pure and Applied Chemistry is a group of Chemists who devised a system of naming that allows for unique names to be applied to organic compounds. There are many compounds that also have common names, but this system allows us to speak a common language when naming these compounds. The simple alkanes above are the simplest examples.
IUPAC - Naming hydrocarbons Problem Hexane C6H14 has 5 isomers. (See right) How do we distinguish between them? Note: these are shorthand notations where each line represents a bond between two carbon atoms IUPAC “Quick” Rules for Alkane Nomenclature 1. Find and name the longest continuous carbon chain. 2. Identify and name groups attached to this chain. (These are called substituents.)3. Number the chain consecutively, starting at the end nearest a substituent group. 4. Designate the location of each substituent group by an appropriate number and name.5. Assemble the name, listing groups in alphabetical order using the full name (e.g. ethyl before methyl). The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing. • Important notes: • a hydrocarbon substituent becomes an alkyl group. (e.g. ethane becomes ethyl) • Some substituents are “active sites” for reactions to occur (e.g. alcohols, ketones, alkenes) – these are then also referred to as functional groups.
IUPAC names for the isomers? n-hexane 2-methyl pentane 3-methyl pentane 2,2 – dimethyl butane 2,3 – dimethyl butane IUPAC “Quick” Rules for Alkane Nomenclature 1. Find and name the longest continuous carbon chain. 2. Identify and name groups attached to this chain. (These are called substituents.)3. Number the chain consecutively, starting at the end nearest a substituent group. 4. Designate the location of each substituent group by an appropriate number and name.5. Assemble the name, listing groups in alphabetical order using the full name (e.g. ethyl before methyl). The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.
IUPAC – Naming Alkenes IUPAC Rules for Alkene and Cycloalkene Nomenclature 1. The ene suffix (ending) indicates an alkene or cycloalkene.2. The longest chain chosen for the root name must include both carbon atoms of the double bond. 3. The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.4. The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.5. In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.6. Substituent groups containing double bonds are:H2C=CH– Vinyl groupH2C=CH–CH2–Allyl group But-1-ene But-2-ene
Functional Groups Functional groups are specific groups of atoms or bonds within a compound that are responsible for characteristic chemical properties of those substances. Amines, Amides, Esters and Nitriles are HL only
Alcohols R-OH Alcohols contain the hydroxyl group (OH) in place of a H atom in a hydrocarbon. Formula – CnH2n+1OH Compound suffix – “anol” A number is used to indicate the location of the hydroxyl on a carbon chain in the same manner previously described. Alcohols follow the same trend in b.p. as the hydrocarbons, but are all higher due to H-bonding. Propan-1-ol
Aldehydes R-CHO Aldehydes contain the carbonyl group (C=O) which is bonded to the last (terminal)carbon in a chain. Formula – CnH2nO Compound suffix – “anal” No numbers are necessary for the naming of aldehydes as the group is on the terminal carbon. Because of the carbonyl, there are permanent dipoles leading to stronger IM forces than alkanes, but weaker than alcohols. Propanal
Ketones R-COR’ Ketones contain the carbonyl group (C=O) which is bonded to a carbon that is not on the terminal end. This placement is how they differ from aldehydes. Formula – CnH2nO Compound suffix – “anone” A number is used to indicate the location of the carbonyl on a carbon chain. Because of the carbonyl, there are permanent dipoles leading to stronger IM forces than alkanes, but weaker than alcohols. Butan-2-one
Carboxylic Acids R-COOH Carboxylic acids contain the carbonyl group (C=O) and the hydroxyl (OH) group. Formula – CnH2nO2 Compound suffix – “anoic acid” These compounds are polar towards the O atoms, away from the H atom, making the H atom available in acid/base rxns. Because of the carbonyl and the hydroxyl, Hydrogen bonding occurs between these molecules. Ethanoic acid
Halides R-X Halogenoalkanes contain the halide functional group, which is a halogen (X)atom in place of a hydrogen. Formula – CnH2n+1X Compound prefixes – “chloro”, “bromo”, “iodo” These compounds are named with the corresponding halogen atom at the beginning with the remainder of the compound named as per the rules for hydrocarbons. Again, a number is used to indicate the position of the halogen on the carbon chain. More than one halogen may be present 2-chloropropane
Primary, Secondary, Tertiary alcohols and halides Primary (10): When a functional group is attached to a carbon that is bonded to only one other carbon atom. Secondary (20): When a functional group is attached to a carbon that is bonded to two other carbon atoms. Tertiary (30): When a functional group is attached to a carbon that is bonded to 3 other carbon atoms. For you to do: Name the three alkyl halides above
What functional groups can you see? Benzene ring Carboxylic acid IBUPROFEN
What functional groups can you see? Carboxylic acid Ester
What functional groups can you see? Carboxylic acid Amine An amino acid
Amines (AHL) R-NH2 Amines contain the amino group (NH2) somewhere in the hydrocarbon chain. Formula – RNH2 Compound suffix – “ylamine” OR Compound prefix – “amino” A number is used to indicate the location of the amino on a carbon chain in the same manner previously described. 1-butylamine
Amides (AHL) R-CONH2 Amides contain the amino group (NH2) and a carbonyl group (C=O). Formula – RCONH2 Compound suffix – “anamide” Amides are the same structure as carboxylic acids with the amine group replacing the hydroxyl. butanamide
Esters (AHL) R-COOR’ Esters contain the carbonyl group (C=O) with an additional O attached to the carbon. Formula – RCOOR’ Compound suffix – “yloate” Esters are named in two parts from the carboxylic acid and alcohol that they are made from. The first part of the name comes from the alcohol and the second from the acid.
Nitriles (AHL) R-CN Nitriles (aka cyanides) contain the cyano group which is a carbon triple bonded to a nitrogen. Formula – RCN Compound suffix – “nitrile” Nitriles are named by their hydrocarbon chain with nitrile added at the end. pentanenitrile