Chapter 10: Organic Chemistry
10.1 Fundamentals of Organic Chemistry
10.1.1 Introduction to Organic Chemistry:
Organic chemistry is the study of carbon compounds. Carbon can form many compounds as carbon can join to make chains and rings (cantenation) and is very stable.
10.1.2 Homologous Series
♦ Understanding: A homologous series is a series of compounds of the same family, with the same general formula, which differ from each other by a common structural unit.
A homologous series is a group of compounds with the same functional group , each compound differs from its adjacent members by a common structural unit (usually –CH2–).
A functional group is the atom(s) in a molecule that are responsible for the primary chemical properties of the molecule- it is also the part of the molecule which reacts.
♦Skill: Identification of different classes: alkanes, alkenes, alkynes, halgogenalkanes, alcohols, ethers, aldehydes, keytones, esters, carboxylic acids, amines, amides, nitriles and arenes.
Each class is a diffrent homologous series, with different functional groups and properties.
|Homologous Series/ Class Name||Functional Group||Functional Group Name||Example||General Name||Name|
|carboxyl||alkanoic acid||propanoic acid|
-X X= Cl/Br/I
(C of C=N
included in chain)
♦Explanation: of the trends in boiling points of members of a homologous series
Properties of homologous series include:
- Members of a homologous series will have similar chemical properties (due to similar arrangement of atoms) however different physical properties.
- As the chain length of the compound increases, the boiling and melting point will too due to more London forces.
- Branching in a molecule will decrease its boiling point as there is a lower surface area for London forces to act.
- The boiling point of straight-chain alkanes will increase when a methylene
(–CH2–) group is added, as the strength of the intermolecular London forces increases as the relative molecular mass of the alkanes increases
♦Skill: Structural formulas can be represented in full and condensed format.
♦Application: Discussion of the structure of benzene using physical and chemical evidence.
Benzene (C6H6) has molecules in a planar, hexaganonal ring of 6 carbons with a hydrogen bonded to each of them.
- Compounds containing a benzene ring are aromatic, and compounds without are aliphatic.
- The functional group in aromatic compounds is the benzene ring as it preforms characteristic chemical reactions.
10.1.3 Naming Hydrocarbons:
♦Application: IUPAC rules in the nomenclature of straight-chain and branched chain
Organic molecules are named according to the International Union of
Pure and Applied Chemistry (IUPAC) system. The following rules should be applied:
- The largest continuous carbon chain dictates the prefix.
- If there are any substituent groups (alkyl groups) , the number of carbon atom they are on should be noted ( using the combination that has the lowest individual numbers)
- Use the appropriate prefix for the number of substituent groups.
- The names of the substituent groups should be arranged in alphabetical order.
|Number of Identical Substituent Groups||Prefix|
Naming Alkenes and Alkynes:
Naming alkenes come in the form alk-X-ene, with X the position on the carbon chain that the C=C bond is.
Alkynes are named the exact same way, (Alk-X-yne) wit X being the position of the triple bond.
Saturated and Unsaturated Compounds:
♦Understanding: Saturated compounds contain single bonds only and unsaturated compounds contain double or triple bonds
Saturated molecules do not contain C=C or C ≡C bonds, unsaturated compounds contain at least one triple or double bond carbon.
- Alkenes and Alkynes are unsaturated compounds as they posses double (C=C) or triple ( C≡C) carbon bonds.
- Benzene is also described as unsaturated as the strucutre could be drawn with three C=C bonds.
- Alkanes are saturated.
10.1.4 Naming Halogenalkanes:
Halgongenalkanes are alkanes that contain a halogen as their functional group.
- Halgonalkanes are named with the formula: x-haloalkane, where x tells the position of the alkane in the chain and halo the prefix for the particular halogen involved.
- e.g 1,2 dicholorobutane
- When there is more than one halogen, they are arranged in alphabetical order, for example 1-bromo,2-chlorobutane
- If there is another substituent group e.g a methyl group, the alphabetical rule still applies.
10.1.5 Naming of Organic Compounds Containing Oxygen
Alcohols are named with the formula alco-X-hol, with X being the position of the OH.
Ethers contain the C-O-C functional group and many ethers have two alkyl groups separated by an oxygen atom.
- The shorter group and oxygen are called an alkoxy group (e.g ethoxy)
- length of the carbon change after the O determine the prefix of the alkoxy group (e.g methoxy, with 1 C atom)
Naming Aldehydes, Keytones, Carboxylic Acids, and Esters:
Aldehydes and keytones are carbonyl compounds and possess the carbonyl C=O functional group.
Carboxylic acids contain the COOH functional group.
- Aldehydes: alkanal
- Keytones: alkan-X-one
- Carboxylic acids: alkanoic acid
In Aldehydes and Carboxylic Acids the carbon in the functional group (CHO or COOH) is numbered carbon 1.
With keytones, the numbering is delegated so that the C=O is given the lowest possible number.
Esters can be named by using the name of the carboxylic acid part of the compound as the suffix and the hydrocarbon group as the prefix.
10.1.6 Primary, Secondary and Tertiary Alcohols:
Alcohols are named primary, secondary or tertiary dependent on the number of carbon atoms attached to the -OH functional group.
Ethanol is a primary alcohol: the carbon atom that the -OH is attached to is only attached to one other other carbon atom- as there are only two carbon atoms in the chain.
Propan-2-ol is a secondary alcohol as it has two carbon atoms attached to the carbon attached to the -OH.
2-methyl-propan-2-ol is a tertiary alcohol, because the carbon bonded to the -OH group is bonded to three other carbon atoms.
Primary, Secondary and Tertiary Halogenalkanes:
Primary, Secondary and Tertiary Amines:
With amines, in the functional group NH2 , the N is the main focus. Thus, a primary amine is where the N is bonded to 1 carbon and 2 Hydrogen, a secondary amine is where the N is bonded to 2 C atoms and 1 H atom, and a tertiary amine is one where the N is bonded to 3 C and no H.
- In a primary amine, the functional group is NH2
- In a secondary amine, the functional group is NHR (where R is an alkyl group)
- In a tertiary amine, the functional group is NR2
Structural isomers are two or more compounds which possess the same molecular formula however have different structural formulas: the atoms are bonded together in a different way/arrangement.
In the figure above, both compounds have the molecular formula C4H10, however one is butane and one is 2-methylpropane.
With a saturated compound, if the longest chain is the same in two compounds they are likely the same, rather than isomers. For example:
Both compounds are pentane.
-In general, branched isomers have a lower boiling point as they prevent the atoms being close together therefore the London forces are weaker and easier to break.
-In the table above, multiple isomers can be made by changing the position of the C=C or by adding an alkyl group.
-Some isomers can have different functional groups. These are sometimes called functional group isomers.