10.1 Introduction

Assessment Objectives Describe the features of a homologous series Predict and explain the trends in boiling points of members of a homologous series Distinguish between empirical, molecular and structural formulas Describe structural isomers as compounds with the same molecular formula but with different arrangements of atoms.

References Moodle Textbook Workbook Videos

Key Terms Hydrocarbon Homologous Series Alkane/alkene/alkyne Functional Group

Assessment Objective Describe the features of a homologous series.

Firstly…… Lets look at some terms………….

Hydrocarbon Hydrocarbons are organic compounds that contain only hydrogen and carbon. Types of hydrocarbons include: Alkanes Alkenes Alkynes Aromatic

Functional Groups As has already been indicated, alkanes are relatively unreactive. For an organic molecule to be reactive it needs something additional. A site of reactivity in an organic molecule is called a functional group. C=C double is a functional group. Other functional groups contain elements other than C or H, notably O, N and Cl.

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Homologous Series Homologous series is a set of compounds whose components differ by a single repeating functional group. In the case of (straight chain) ALKANES, their general formula is: C n H 2n+2

An Example of an Homologous Series

Assessment Objective Predict and explain the trends in boiling points of members of a homologous series.

Hypothesis What do you predict will happen to the boiling point as you increase the size of the molecule? Why??

Activity Worksheet.

In a homologous series there is a gradual increase in boiling points as the # of carbon atoms increases. Cross reference with 4.3.

Melting Points and Boiling Points Boiling points of unbranched alkanes increase smoothly with number of carbons Melting points increase in an alternating pattern according to whether the number of carbon atoms in the chain is even or odd

Assessment Objective Distinguish between empirical, molecular and structural formulas.

Structural Formula Note Each carbon has 4 bonds This is a form of a condensed structural formula This is a full structural or displayed formula. All the bonds are shown including all the hydrogen atoms

Molecular Formula C 6 H 12 is a molecular formula. It does not give much information as this could be any one of several different compounds

Empirical Formula This is the simplest whole number ratio For example if the molecular formula of glucose is C 6 H 12 O 6 Then the empirical formula is CH 2 O This is the empirical formula for many carbohydrates

General Formula This are used for homologous series The alkanes C n H 2n+2 The alkenes C n H 2n The alkanols or alcohols C n H 2n+1 OH

Assessment Objective Describe structural isomers as compounds with the same molecular formula but with different arrangements of atoms.

Activity How many different ways can you draw the structural formula of butane? General formula C n H 2n+2 Molecular Formula C 4 H 10 What about pentane?

Activity Molecular Modeling Kit

The number of isomers possible for a given molecular formula increases rapidly with the number of carbons

Structural Isomers Compounds with the same molecular formula but with different arrangements of atoms. These isomers will have different physical properties. So how do we name them (and distinguish between them)???????

Assessment Objectives Deduce structural formulas for the isomers of the non-cyclic ALKANES up to C Apply IUPAC rules for naming the isomers of the non-cyclic alkanes up to C 6.IUPAC

Naming Organic Compounds Originally compounds were named based on their source or use Many organic compounds were given common name which are still in use However many ambiguities resulted With the large number of organic compounds, a method for systematically naming them is very important.

IUPAC Names The International Union of Pure and Applied Chemists (IUPAC) developed a system for naming organic compounds. This system eliminated many of the ambiguities that plagued earlier naming systems. Common names for many substances are still widely used

Naming Organic Molecules

A series of prefixes are used to designate the number of carbon atoms in a carbon chain. meth C1 hex C6 eth C2 hept C7 prop C3 oct C8 but C4 non C9 pent C5 dec C10

Naming Straight Chain Alkanes

Naming Branched Chain Alkanes 1. Locate the longest continuous chain of carbons; this is the parent chain and determines the parent name. 2. Number the longest chain beginning with the end of the chain nearer the substituent 3. Designate the location of the substituent

Examples

4. When two or more substituents are present, give each substituent a number corresponding to its location on the longest chain

Examples

5. Substituents are listed alphabeticall y. When two or more substituents are identical, use the prefixes di-, tri-, tetra- etc. Commas are used to separate numbers from each other The prefixes are used in alphabetical prioritization When two chains of equal length compete to be parent, choose the chain with the greatest number of substituents

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Assessment Objectives Deduce structural formulas for the isomers of the straight-chain alkenes up to C Apply IUPAC rules for naming the isomers of the straight-chain alkenes up to C 6.

Alkenes are named by finding the longest chain containing the double bond and changing the name of the corresponding parent alkane from -ane to - ene The compound is numbered to give one of the alkene carbons the lowest number

The double bond of a cylcoalkene must be in position 1 and 2

Please draw all the structural isomers (apart from cyclic isomers) for C4H10, C5H12 and C6H14 and name them.

Assessment Statement Deduce structural formulas for compounds containing up to six carbon atoms with one of the following functional groups: alcohol, aldehyde, ketone, carboxylic acid and halide Apply IUPAC rules for naming compounds containing up to six carbon atoms with one of the following functional groups: alcohol, aldehyde, ketone, carboxylic acid and halide.

47 Activity Draw structural formula and name: ….. CH 3 CH(OH)CH 3 CH 2 (Cl)CH 2 CHO HCOOH CH 3 (CH 2 ) 2 OCH 3 CCl 3 COOH CH 3 CCl 2 CH(OH)CH 2 CH 3

Assessment Statement Identify the following functional groups when present in structural formulas: amino (NH2), benzene ring and esters (RCOOR).

49 You need to recognize the benzene structure in structural formulas This is the general layout with a perfect hexagon. In this particular diagram you do not see the double bonds.

50 Two Lewis structures for the benzene ring.

51 Shorthand notation for benzene rings.

52 Some common mono-substituted benzene molecules Toluene, sometimes you see this on marker pens ”contains no toluene” Has the condensed structural formula C 6 H 5 CH 3

54 Name each of the following CH 3 CH 2 NH 2 CH 3 COOCH 2 CH 3 C 2 H 5 COOCH 3 CH 3 NH 2 C 3 H 8 COOCH 2 CH 3

55 Naming esters The alcohol part of the name comes first and the carboxylic part second For example CH 3 COOCH 3 is made from CH 3 COOH and CH 3 OH. i.e Ethanoic acid and methanol It’s name is Methyl ethanoate

Assessment Statement Identify primary, secondary and tertiary carbon atoms in alcohols and halogeno-alkanes.

Primary alcohols have –RCH 2 OH Secondary alcohols have –R 2 CHOH Tertiary have alcohols –R 3 COH This means primary have 1 ‘different group attached, we usually call this an R group. Secondary have 2 R groups and tertiary have 3 R groups attached to the C next to the functional group

61 If two identical groups occur on the same side of the double bond the compound is cis If they are on opposite sides the compound is trans Several alkenes have common names which are recognized by IUPAC

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