Organic Chemistry. A. Introduction

Transcription

1 Organic Chemistry A. Introduction 1. Organic chemistry is defined as the chemistry of CARBON compounds. There are a huge number of organic compounds. This results from the fact that carbon forms chains involving several carbon atoms linked to each other in a straight-line fashion, in a circular pattern, or in a branched pattern. In addition, the carbon atoms may form single, double, or triple bonds to neighbouring atoms. 2. Organic compounds are found in petroleum, natural gas, and all living things. The largest industry involving organic chemistry is the manufacture of petrochemicals. Petroleum is the starting material for a vast range of products. Petroleum is separated ( fractioned ) and refined for use in gasoline and oil, while other fractions of petroleum are chemically altered to serve as raw materials for a huge array of industrial processes such as the manufacture of plastics, solvents, pharmaceuticals, and personal care products.

2 UNIT X ORGANIC CHEMISTRY 2 B. Alkanes 1. A carbon atom can form bonds to four other atoms (carbon has a valence of four). A HYDROCARBON is a compound containing only hydrogen and carbon. There are many ways to represent a hydrocarbon formula, depending on how compact one wants to write the formula. EXAMPLE X.1 REPRESENTING HYDROCARBONS Problem: Write the structure of propane, C 3 H 8 as full structure, condensed structure, molecular formula, and carbon skeleton. Solution: Full Structure H H H H C C C H H H H Condensed structure CH 2 Molecular formula C 3 H 8 Carbon skeleton C C C

3 UNIT X ORGANIC CHEMISTRY 3 2. ALKANES (A HOMOLOGOUS SERIES) H methane = CH 4 ethane = C 2 H 6 H C H H H H H H C C C H H H H propane = C 3 H 8 butane = C 4 H 10 H H H C C H H H H H H H H C C C C H H H H H Notice that each carbon forms four bonds. The number of H s attached is 4 minus the numbers of C s attached. methane 1 CH 4 ethane 2 C 2 H 6 propane 3 C 3 H 8 CH 2 butane 4 C 4 H 10 CH 2 CH 2 pentane 5 C 5 H 12 CH 2 CH 2 CH 2 hexane 6 C 6 H 14 CH 2 CH 2 CH 2 CH 2 heptane 7 C 7 H 16 CH 2 CH 2 CH 2 CH 2 CH 2 octane 8 C 8 H 18 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 nonane 9 C 9 H 20 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 decane 10 C 10 H 22 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 An ALKANE is a hydrocarbon in which all the carbon atoms are connected by single bonds.

4 UNIT X ORGANIC CHEMISTRY 4 2. Each of the molecules differs by the number of carbon atoms linked to one another to form a CARBON CHAIN. A series of structures that differ from each other by one structural unit, in this case CH 2, are called a HOMOLOGOUS SERIES. Because the chain of carbon atoms extends in a straight-line they are called STRAIGHT-CHAIN or UNBRANCHED hydrocarbons. The names of the all the above hydrocarbons end in ANE because they are ALKANES. Alkanes are said to be SATURATED hydrocarbons because each carbon atom is bonded to the maximum possible number of other atoms. Each of the single bonds between carbon atoms is able to rotate freely, leading to a highly flexible chain which can take many shapes. The following molecules all represent heptane, C 7 H 16 CH 2 CH 2 CH 2 CH 2 CH 2 CH CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 0 Assign #1 3. A hydrocarbon can also have SIDE BRANCHES which are also hydrocarbon chains. The attached groups are called ALKYL GROUPS. CH CH 2 CH 2 CH 2 CH 2 An ALKYL GROUP is an alkane, which has lost one hydrogen atom.

5 UNIT X ORGANIC CHEMISTRY 5 An alkyl group is named by changing the ANE ending of the original hydrocarbon to YL. ORIGINAL HYDROCARBON ALKYL GROUP methane = CH 4 methyl = ethane = ethyl = CH 2 propane = CH 2 propyl = CH 2 CH 2 butane = CH 2 CH 2 butyl = CH 2 CH 2 CH 2 4. When an alkyl group is attached to another hydrocarbon, the resulting molecule is called a SUBSTITUTED HYDROCARBON or a BRANCHED HYDROCARBON. NAMING A SUBSTITUTED HYDROCARBON: i) First find the longest continuous chain of carbon atoms. This longest chain is called the PARENT hydrocarbon. (Look at branch points.) C C C C C C C C C C C C 9 Carbons C C C C C C C C C C C C C C C C Assign 2bd 10 carbons Write the CARBON NUMBER at which the alkyl group is attached followed by a dash. i Name the alkyl group.

6 UNIT X ORGANIC CHEMISTRY 6 iv) Name the longest or parent hydrocarbon to which the alkyl group is attached. (The carbon atoms in the parent hydrocarbon are numbered consecutively from the end of the hydrocarbon which gives the lowest possible set of numbers (address) to the attached groups. Assign 3-6ace v) If more than one different alkyl group is attached to the hydrocarbon, then list the alkyl groups ALPHABETICALLY preceded by its number and a dash. vi) If an alkyl group is repeated, list each carbon number where the repeated group is attached, separated by commas and the prefix di, tri, tetra, etc. to show how many identical groups are attached. EXAMPLE X.2 NAMING SUBSTITUTED HYDROCARBONS Problem: Name the following substituted hydrocarbons. Solution: C C C C C C C C C C 3 ethyloctane C C C C C C C C C C 3 ethyl 5 methylheptane C C C C C C C C C C C C C C Assign 7-9 ace 3 ethyl 4,4,6 trimethylnonane

7 UNIT X ORGANIC CHEMISTRY 7 C. Structural Isomers 1. It is possible for two or more molecules to have the same molecular formula (same number and types of atoms) but different arrangement of atoms (structure). All of the following molecules have the molecular formula C 5 H 12. CH 2 CH 2 CH 2 Pentane CH CH 2 2 methyl butane C dimethyl propane STRUCTURAL ISOMERS are compounds which have the same molecular formula but a different arrangement of atoms. Assign Hydrocarbons which connect in a head to tail CIRCLE are called CYCLIC HYDROCARBONS or CYCLOALKANES. H 2 C CH 2 \ / CH 2 cyclopropane H 2 C CH 2 H 2 C CH 2 cyclobutane cyclopentane cyclohexane Assign 14

8 UNIT X ORGANIC CHEMISTRY 8 NAMING CYCLOALKANES: i) follow the same rules as straight chain alkanes, except that a single substituent does not use a number to indicate the position of attachment. If there is more than one substituent, the first substituent is assumed to be at the 1 position and the remaining substituents are numbered either clockwise or anticlockwise to have the lowest set of overall values. EXAMPLE X.3 NAMING CYCLOALKANES Problem: Name the following cycloalkanes. Solution: C methyl cyclopentane C C C / C 2 ethyl-1,4 dimethyl cyclohexane Ignore di, tri when writing the order Assign 15-16ace

9 UNIT X ORGANIC CHEMISTRY 9 D. Alkyl Halides 1. There are some organic compounds where the hydrogens are substituted by a halogen ( F, Cl, Br or I). These compounds are called ALKYL HALIDES. NAMING ALKYL HALIDES: i) Attached F, Cl, Br and I atoms are called fluoro, chloro, bromo and iodo groups. Use numbers to indicate the position of attachment on the hydrocarbon chain. i If more than one of the same kind of halogen is present, use the prefixes di, tri, tetra, etc. If a compound contains both alkyl and halo groups, list the attached groups in alphabetical order. Start numbering from the end that gives the lowest set of numbers. EXAMPLE X.4 NAMING ALKYL HALIDES Problem: Name the following alkyl halides. Solution: CH CH 2 F 2 fluoro butane CH CH 2 CH Cl Cl 2,4 dichloro pentane CH 2 CH C CH 2 Br F 2 bromo 3 ethyl 3 fluoro pentane

10 UNIT X ORGANIC CHEMISTRY PROPERTIES OF ALKYL HALIDES Alkyl halides tend to be insoluble in water. Compounds with many fluorine atoms tend to be unreactive. Chloro and bromo compounds are susceptible to chemical attack, but require relatively drastic conditions. Iodo compounds are more reactive. Assign 17-20ace

11 UNIT X ORGANIC CHEMISTRY 11 E. Multiple Bonds 1. Carbon atoms can form up to four bonds but it can form multiple bonds with other carbon atoms. When a carbon shares 4 electrons with a neighbouring carbon a DOUBLE BOND is formed and when is shares 6 electrons with a neighbouring carbon a TRIPLE BOND is formed. An ALKENE is an organic compound containing a carbon carbon double bond. An ALKYNE is an organic compound containing a carbon carbon triple bond. NAMING ALKENES AND ALKYNES: i) If a double bond is present, change the ANE ending of the parent hydrocarbon to ENE. If a triple bond is present change the ANE ending of the parent hydrocarbon to YNE. i Use a number to indicate the lower numbered carbon atom involved in the bond. The number goes immediately in front of the name of the parent hydrocarbon, separated by a hyphen. Number the parent hydrocarbon to give the double/triple bond the lowest possible number. If the number is the same starting from either end, start the numbering from the end closest to the 1 st branch point (where a group is attached).

12 UNIT X ORGANIC CHEMISTRY 12 EXAMPLE X.5 NAMING ALKENES AND ALKYNES Problem: Name the following alkenes and alkynes. Solution: H CH 2 \ / C = C / \ H H CH C CH 2 = CH CH 1 butene propyne 3 methyl 1 butene 2. REMEMBER: single bonds double bonds triple bonds ANE ENE YNE Assign 21-25ace Alkenes and alkynes are called UNSATURATED hydrocarbons because they have less hydrogen atoms than equivalent alkanes. Alkanes are said to be saturated hydrocarbons because they contain the maximum number of hydrogens possible. 3. Whereas alkanes have flexible structures, alkenes have very rigid structures. The double bonds lock the structure to prevent the attached atoms from twisting around the double bond. The triple bond in alkynes is also very rigid. For an alkane, these two molecules are identical because the single bond is free to rotate. H 3 C CH CH CH 2 2,3 dimethyl pentane H 3 C CH CH CH 2 2,3 dimethyl pentane

13 UNIT X ORGANIC CHEMISTRY 13 Because the double bond in an alkene cannot rotate or twist, these two molecules are chemically different. H 3 C C = C CH 2 2,3 dimethyl cis 2 pentene Notice that in the alkane both molecules have the same name because they are the same molecule but in the alkene one is named CIS and the other TRANS. 4. CIS TRANS isomerism is possible whenever a molecule has: i) a double bond present, AND H 3 C C = C CH 2 2,3 dimethyl trans 2 pentene groups (other than a hydrogen atom) attached to each of the carbons involved in the double bond. In a CIS isomer, the two groups are on the SAME SIDE of the double bond. H 3 C \ / C = C / \ H H both s are on the same side Assign 26-28ace In a TRANS isomer, the two groups are TRANSVERSE to each other (that is, on opposite sides of the double bond). H 3 C H \ / C = C / \ H the s are on opposite sides

14 UNIT X ORGANIC CHEMISTRY 14 F. Aromatic Compounds 1. Benzene, C 6 H 6, is an important molecule having the following structure. The ring like structure of benzene can be written in either of two RESONANCE STRUCTURES, differing only in the placement of the double bonds. Each resonance structure consists of alternating single and double bonds. Benzene is frequently represented as follows. Benzene 2. The benzene ring, also known as an AROMATIC RING, is present in a large number of molecules and many molecules contain two or more aromatic rings joined together. An AROMATIC MOLECULE is a molecule containing one or more benzene rings. NAMING AROMATIC MOLECULES: i) The naming of simple aromatic compounds formed by adding groups to a benzene ring is almost identical to the naming procedure used for cyclic hydrocarbons. When the benzene ring is attached to another hydrocarbon as a substituent or group it is called a PHENYL group.

15 UNIT X ORGANIC CHEMISTRY 15 EXAMPLE X.6 NAMING AROMATIC MOLECULES Problem: Name the following aromatic molecules Solution: CH 2 CH 2 ethyl benzene H 3 C \ 4-ethyl-1,2-dimethylbenzene CH CH 2 2 phenyl butane Assign 29-31ace

16 UNIT X ORGANIC CHEMISTRY 16 G. Functional Groups 1. On some organic molecules, one or more of the hydrogens may be substituted by an atom or a group of atoms. These substitutions are called FUNCTIONAL GROUPS. A FUNCTIONAL GROUP is a specific group of atoms which exists in a molecule and gives a molecule an ability to react in a specific manner or gives it special properties. Hydrocarbons have a limited range of properties and uses. Functional groups allow the addition of specific properties to a molecule. For example, by carefully choosing the functional group present in a molecule, a chemist can: i) make a molecule act as a base, an acid, or both; i iv) give the molecule a particular solubility; give a molecule a pleasant or unpleasant smell; make a molecule react with specific chemicals; v) make a molecule explosive.

17 UNIT X ORGANIC CHEMISTRY Different FUNCTIONAL GROUPS a) ALCOHOL An ALCOHOL is an organic compound containing an OH group. NAMING AN ALCOHOL: i) Number the hydrocarbon chain to give the LOWEST possible number to the OH group. Place the number immediately before the name of the parent hydrocarbon separated by a dash. i Indicate the presence of an OH group by changing the e ending of the hydrocarbon chain to ol. OH methanol CH 2 OH ethanol CH CH 2 OH 2 butanol CH CH 2 CH 2 CH CH 2 OH 6 methyl 3 heptanol Assign 32-33ace b) ALDEHYDES An ALDEHYDE is an organic compound containing a C=O group at the end of hydrocarbon chain. The aldehyde group actually looks like CHO. O C H or simply

18 UNIT X ORGANIC CHEMISTRY 18 NAMING ALDEHYDES: i) Change the e ending of the parent hydrocarbon to al. If there are substituents attached, they are numbered starting from the CHO group. O H C H methanal (formaldehyde) CHO ethanal CHO benzenal CH 2 CH 2 CH CHO 2 methyl pentanal c) KETONES A KETONE is an organic compound containing a C=O group at a position OTHER THAN AT THE END of a hydrocarbon chain. The ketone group is represented by CO. NAMING KETONES: i) Number the hydrocarbon chain to give the LOWEST possible number to the CO group. Place the number immediately before the name of the parent hydrocarbon separated by a dash.

19 UNIT X ORGANIC CHEMISTRY 19 i Change the e ending of the parent hydrocarbon to one. O C or CO CH 2 COCH 2 CH 2 propanone (acetone) O 3 hexanone cyclohexanone d) ETHERS An ETHER is an organic compound in which an oxygen joins two hydrocarbon groups. The ether group is represented by O. NAMING ETHERS: i) Name the shorter hydrocarbon chain. Replace the ane with oxy. i Number the parent hydrocarbon so that the ether group has the LOWEST possible number. Use a number separated by a dash to indicate the location of the ether group. CH 2 O CH 2 ethoxy ethane O CH 2 CH 2 1 methoxy propane C CH 2 CH 2 O 1 methoxy 3,3 dimethylbutane

20 UNIT X ORGANIC CHEMISTRY 20 e) AMINES An AMINE is an organic compound containing an NH 2 group. NAMING AMINES: i) Number the parent hydrocarbon so that the amine has the LOWEST possible number. Name the NH 2 group amino and indicate the location of the amine group by a number followed by a dash. CH 2 NH 2 amino ethane CH CH 2 NH 2 2 amino butane f) AMIDES An AMIDE is an organic compound containing a CONH 2 group. O C NH 2

21 UNIT X ORGANIC CHEMISTRY 21 NAMING AMIDES: i) Number the parent hydrocarbon from the CONH 2 group. Remove the "e ending and add amide to the end of the name. CONH 2 ethanamide CH 2 CH 2 CH 2 CH 2 CONH 2 hexanamide C CH 2 CONH 2 3,3 dimethylbutanamide g) CARBOXYLLIC ACIDS A CARBOXYLLIC ACIDS is an organic compound containing a COOH group. NAMING CARBOXYLLIC ACIDS: O C OH i) Number the parent hydrocarbon from the COOH group. Remove the "e ending and add oic acid to the end of the name. COOH HCOOH CH 2 CH 2 COOH ethanoic acid (acetic acid) methanoic acid (formic acid) butanoic acid (butyric acid)

22 UNIT X ORGANIC CHEMISTRY 22 h) ESTERS An ESTER is an organic compound containing a COO group. NAMING ESTERS: O C O i) The hydrocarbon attached directly to the carbon side of the COO group has its e changed to oate. The hydrocarbon chain attached to the oxygen side of the COO group is named as an alkyl group. CH 2 CH 2 COO methyl butanoate HCOO CH 2 CH 2 butyl methanoate CH 2 COO CH 2 ethyl propanoate COO CH 2 CH 2 propyl ethanoate SUMMARY OF FUNCTIONAL GROUPS NAME FUNCTIONAL GROUP NAME FUNCTIONAL GROUP alkene C = C ether O alkyne C C amine NH 2 halide F, Cl, Br, I amide CONH 2 alcohol OH carboxyllic acid COOH aldehyde CHO ester COO ketone CO aromatic ring Assign 37 odd That s all folks!