Organic chemistry

Organic Chemistry Organic means living Hydrocarbons contain hydrogen and carbon atoms Organic Chemistry is the study of carbon chemicals that are natural and artificial. The bonding in hydrocarbons is covalent so bonding between molecules is weak. The structure is molecular.

CH4 (GAS), C8H18 (LIQUID), C30H62 (SOLID) Homologous series This is a series of compounds which all contain the same functional group, and have similar chemical properties.  ALKANES ALKENES ALCOHOLS CH4 CH2 =CH2 CH3OH CH3-CH3 CH2 =CH –CH3 CH3CH2OH Each has a general formula: ALKANES: CnH2n+2 The members of the series differ by the number of CH2 units. CH3-CH3, CH3-CH2-CH3, CH3-CH2-CH2-CH3 Graduation in physical properties:  eg: boiling points. CH4 (GAS), C8H18 (LIQUID), C30H62 (SOLID)

IUPAC The International Union of Pure and Applied Chemistry Why? Historical names (e.g. acetic acid, formic acid) meant nothing to other scientists in different countries

IUPAC Rules for Alkane Nomenclature  1.   Find and name the longest continuous carbon chain. AKA parent chain  2.   Identify and name groups attached to this chain.  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.      The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.

Naming Alkanes General formula CnH2n+2 Saturated compounds: each carbon is bonded to the maximum possible number of atoms.

“Prefix + Root + Suffix” Find the main chain (1 = meth, 2 = eth, 3 = prop, 4 = but, 5 = pent, 6=hex) Determine your suffix (Alkane = ane) Number the main chain. Start at the end that gives branches the lowest numbers. Name each branch as an alkyl group (methyl, ethyl, propyl etc.), and placing a position number in front. Note: always put commas between numbers, and hyphens between numbers and letters.

GENERAL FORMULA CnH(2n+2) ALKANES SATURATED HYDROCARBONS – contain maximum amount of hydrogen - only single bonds (no multiple bonds) NAMING ALKANES No of C atoms Prefix 1 Meth 2 Eth 3 Prop 4 But 5 Pent 6 Hex 7 Hept 8 Oct All alkanes end with ‘ANE’. All belong to the same HOMOLOGOUS series GENERAL FORMULA CnH(2n+2)

Examples: C H Methane CH4 C H Ethane C2H6

Alkyl Groups Branches on carbon chains H H C CH3 methyl H H H H C C CH2CH3 ethyl H H Hrw 651 z5e 1077 An alkyl group is composed of one or more carbon atoms attached to a carbon chain. An alkyl group is derived from an alkane by removing one hydrogen. The ending –ane of the alkane is changed to –yl. The carbon branch from methane is the methyl group. The carbon branch from ethane is the ethyl group.

Name these molecules 3-ethyl-3,4-dimethylhexane

STRUCTURES OF ALKANES METHANE CH4 Bond Angle 109.5o Shape Tetrahedral H C H Can be illustrated as:

ETHANE. Molecular formula C2H6 Structural formula: CH3 CH3 or H H H C C H H H

PROPANE. Molecular formula: C3H8 Structural formula: CH3 CH2 CH3 or H H H H C C C H H H H Both ethane and propane are “straight” chain molecules BUT!! Bonds are NOT 90o molecules are NOT STRAIGHT!!! Schematic formula

Give the names of the following alkanes CH3 CH2 CH CH2 CH3 CH3 (b) CH3 CH CH2 CH CH3 CH3 CH3 (c) CH3 C(CH3)2 CH2 CH(CH3) CH2 CH3 (d) CH3CH2CH(CH3)C(CH3)3

Give the names of the following alkanes CH3 CH2 CH CH2 CH3 CH3 (b) CH3 CH CH2 CH CH3 CH3 CH3 (c) CH3 C(CH3)2 CH2 CH(CH3) CH2 CH3 (d) CH3CH2CH(CH3)C(CH3)3 3-methyl pentane 2,4-dimethylpentane 2,2,4-trimethyl hexane 2,2,3-trimethylpentane

Cyclic Alkanes When C atoms bond together to form a ‘ring’ – known as a ‘cyclic’ structure. Example What is the molecular formula of this alkane? How does the molecular formula compare to the general formula for alkanes? Why does it belong to the series of alkanes? Can you think of a name for this molecule Illustrate the cyclic structures of (a) C4H8 and (b) C5H10 and name the molecules. CYCLOHEXANE

Commas and dashes Use commas between numbers Use dashes between numbers and letters And one other thing; when arranging your substituent groups in alphabetical order the di, tri, tetra, etc do not count

Correct the mistakes You have 1 minute to discuss with a partner all the mistakes in the naming of the following compounds

4-methyl-3-4-dichloro-3-bromo-pentane Name B: Cl Cl H3C C C CH2 CH3 CH3 Br Name A: 4-methyl-3-4-dichloro-3-bromo-pentane Name B: 3-bromo-3,4-dichloro-4-methyl-pentane

4-methyl-3-4-dichloro-3-bromo-pentane Not alphabetical Name B: 3-bromo-2,3-dichloro-2-methylpentane Key Incorrect number Dash or comma Cl Cl 1 4 2 3 H3C C C CH2 5 CH3 CH3 Br Name A: 4-methyl-3-4-dichloro-3-bromo-pentane Not alphabetical Name B: 3-bromo-3,4-dichloro-4-methyl-pentane

Worked example 1 1. 6 carbons in the longest chain  hexane  2.   has 2 chloro- groups  dichloro Has a methane group  methyl  3.   Number the chain (see diagram)   4.   1,2-dichloro- 4-methyl  5.   1,2-dichloro-4-methylhexane Remember: when arranging your substituent groups in alphabetical order the di, tri, tetra, etc do not count 1 6 2 3 2 4 1 3 5

Isomers Same molecular formula Same number and types of atoms Different arrangement of atoms Hwr 631; z5e 983 Structural isomers are compounds that have the same molecular formula with different arrangements of the atoms.

Examples of Isomers CH3 The formula C4H10 has two different structures CH3CH2CH2CH3 CH3CHCH3 Butane 2-methylpropane When a CH3 is is used to form a branch, it makes a new isomer of C4H10. Hwr 631 z5e 984

Structural Isomers pp Compounds that have the same molecular formula, but different molecular structures, are called structural isomers Butane and 2-methylpropane on previous slide. Also have different properties, such as b.p., m.p., and reactivity Hrw 631; z5e 1068

Geometric Isomers pp There is a lack of rotation around a carbon to carbon multiple bond has an important structural implication Two possible methyl arrangements: 1. trans configuration - substituted groups on opposite sides of double bond 2. cis configuration - same side Hrw 632; z5e 1060

Geometric Isomers pp Differ only in the geometry of their substituted groups Like other structural isomers, have different physical and chemical properties Hrw 632; z5e 1059

Geometric Isomers of 1,2-dichloroethene Cl Cl H Cl C=C C=C H H Cl H cis trans Rigid structure so these are isomers with different properties. Hrw 632; z5e 1059

Geometric Isomers of chloroethene? pp H Cl H H C=C C=C H H H Cl Rigid structure BUT both carbons do NOT have two DIFFERENT groups attached to them. These are just rotated in space, but are the same. Hrw 632; z5e 1059

Nongeometric versions of 1,2-dichloroeth”ene” pp Cl Cl H Cl C--C C--C H H Cl H Non-rigid structure so these are NOT isomers. (The 3rd hydrogen on each carbon is not shown) Hrw 632; z5e 1059

BUTANE & ISOMERS. Molecular formula: C4H10 - can have two different structures “Straight” chain. CH3 CH2 CH2 CH3 BUTANE Schematic formula: Branched chain CH3 CH CH3 CH3 METHYL PROPANE branch Isomers Compounds that have the same molecular formula but different structural formula.

TASK: Illustrate the structures of the three different isomers of C5H12.

Names & Structures Examples CH3 CH3 CH CH2 CH3 2- methylbutane CH3 CH3 C CH3 2,2 – dimethyl propane TASK: illustrate the structures of: 2-methylpentane. 2,3 – dimethylbutane. 2,2,3 -trimethylpentane CH3CH(CH3)CH2CH2CH3 CH3CH(CH3)CH(CH3)CH3 CH3C(CH3)2CH(CH3)CH2CH3

Alkenes CnH2n Ethene C2H4 A by-product of CRACKING an Alkane Used for making polymers C=C is more reactive than C-C The molecule is unsaturated and the double bonds allow addition polymerisation. C H Ethene C2H4

Structure of Alkenes The shape around the double bond is planar. The bond angle around the double bond is 120o C C  bond  PLANAR 120o Represented as C C

Examples of Alkenes H H C C ………………, C2H4 H H OR ……………………. PROPENE CH2 CH CH3 TASK: Use ball & stick models or sketches to construct and name 3 different structures for C4H8 each one with one double bond.

Examples of Alkenes H H C C H H ETHENE, C2H4 OR CH2 CH2 H H C C H CH3 PROPENE CH2 CH CH3 TASK: Use ball & stick models or sketches to construct and name 3 different structures for C4H8 each one with one double bond. CH3CH2CH CH2 BUT-1-ENE CH3C CH2 CH3 METHYL PROPENE CH3CH CHCH3 BUT-2-ENE

More Alkenes Illustrate structures of the following alkenes: Pent-1-ene Hex-3-ene 2-methylbut-1-ene Cyclohexene Name the following alkenes CH3CH CHCH2CH3 CH2 CHCH(CH3)CH2CH3 CH3CH(CH3)CH CHCH2CH3 (CH3)3CCH C(CH3)2

More Alkenes Illustrate structures of the following alkenes: Pent-1-ene CH2 CHCH2CH2CH3 Hex-3-ene CH3CH2CH CHCH2CH3 2-methylbut-1-ene CH2 C(CH3)CH2CH3 Cyclohexene Name the following alkenes CH3CH CHCH2CH3 Pent-2-ene 3-methylpent-1-ene CH2 CHCH(CH3)CH2CH3 2-methylhex-3-ene CH3CH(CH3)CH CHCH2CH3 (CH3)3CCH C(CH3)2 2,4,4-trimethylpent-2-ene

GEOMETRIC ISOMERS There is no rotation about the double bond. GEOMETRIC ISOMERISM each C atom in the double bond has two different atoms/groups attached. BUT–2-ENE CH3 CH CH CH3 CH3 H C C H CH3 CH3 CH3 C C H H trans but-2-ene cis but-2-ene Geometric isomerism is a form of STEREOISOMERISM – Same molecular and structural formula but atoms are arranged differently in space

Alkynes H-C≡C-H Ethyne Very reactive Triple bond unstable! Attracts electrophiles. H-C≡C-CH3 propyne H-C≡C-CH2-CH3 But–1-yne CH3-C≡C-CH3 But–2-yne