Chapter 20

Organic Chemistry

History and Scope

Early chemists believed that molecules derived from animal or plant sources were created by some "vital force". The vital source theory held that organic molecules could only come from living sources. In 1828 Friedrich Wöhler produced urea (H2N-CO-NH2), an organic molecule, from the reaction of cyanic acid (HCNO) and ammonia (NH3). Since both cyanic acid and ammonia can be produced from nonliving sources and urea is a product of the metabolism of animals, urea was the first organic molecule produced from nonliving source. This was the downfall of the vial force theory.

Classification of Organic Molecules

Organic molecules are classified by their "functional groups". A functional group is an atom or group of atoms bonded in a particular configuration.

Classes of organic molecules: "R" represents any hydrocarbon.

Alkane R-H

Alkene C=C with 2 H and/or C atoms bonded to each carbon

Alkyne C=C with 1 H or C atom bonded to each carbon

Alkyl halide R-X Where X is a halogen

Alcohol R-OH Alcohols have an -OH group somewhere in the molecule

Ether R-O-R' Ethers have an O bonded to two carbons

O

Aldehyde R-C-H Aldehydes have a double bonded O at the end of a chain

O

Keytone R-C-R Keytone have a double bonded O within a carbon chain

O

Carboxylic acid R-C-O-H Organic acids have a double bonded O and OH at end of chain

O O

Ester R-C-O-R' Esters have a -C-O group within the carbon chain

Think 3-D

The carbon atom makes 4 bonds with other atoms. Consider the following molecules:

H

H-C-H methane

H

Carbon with 4 atoms attached is tetrahedral.

H

C=O formaldehyde

H

Carbon with three atoms attached is trigonal planar.

O=C=O carbon dioxide

Carbon with two atoms attached is linear.

Most atoms in organic molecules always have the same number of bonds.

Atom Number of bonds Examples of bonding

Haolgens 1 F- Cl- Br- I-

Hydrogen 1 H-

Oxygen 2 O= -O-

Nitrogen 3 N= -N= -N-

Carbon 4 -C= =C= -C= -C-

When drawing organic molecules keep the above bonding numbers.

Alkanes CnH2n+2

Name Formula Condensed structural formula

Methane CH4

Ethane C2H6 CH3CH3

Propane C3H8 CH3CH2CH3

Butane C4H10 CH3CH2CH2CH3

Pentane C5H12 CH3CH2CH2CH2CH3

Hexane C6H14 CH3CH2CH2CH2CH2CH3

Heptane C7H16 CH3CH2CH2CH2CH2CH2CH3

Octane C8H18 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane C9H20 CH3CH2CH2CH2CH2CH2CH2CH2CH3

Decane C10H22 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Structural Isomerism

Structural isomers have the same formula but different structures.

Problem:

How many different compounds can be made for butane C4H10?

Draw each compound.

Problem:

How many different compounds can be made for butane C5H12?

Draw each compound.

Organic Nomenclature

Substituent Formula Condensed structural formula

Bromo Br-

Chloro Cl-

Fluoro F-

Iodo I-

Methyl CH3-

Ethyl C2H5- CH3CH2-

Propyl C3H7- CH3CH2CH2-

Butyl C4H9- CH3CH2CH2CH2-

Pentyl C5H11- CH3CH2CH2CH2CH2-

Hexyl C6H13- CH3CH2CH2CH2CH2CH2-

Heptyl C7H15- CH3CH2CH2CH2CH2CH2CH2-

Octyl C8H17- CH3CH2CH2CH2CH2CH2CH2CH2-

Nonyl C9H19- CH3CH2CH2CH2CH2CH2CH2CH2CH2-

Decyl C10H21- CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2-

Note: Just replace -ane with -yl to name a hydrocarbon as a substituent group.

To name many of the billions of organic compounds the following nomenclature rules can be used.

1 Select the longest continuous carbon chain as the parent molecule.

2 Number the carbon atoms in the longest continuous carbon chain giving the lowest number to substituent groups or functional groups.

3 Name each substituent group in alphabetic order.

4 When the same substituent group occurs more than once, indicate the position of each substituent group and give the total number of each substituent group by a prefix (di, tri, tetra, penta, hexa, hepta, octa, nona, deca).

Alkane Reactions

Alkanes, as all hydrocarbons burn to give CO2 and H2O.

Alkanes undergo halogenation in the presence of ultraviolet light.

R-H + Cl2 ---> R-Cl + HCl

Demo:

Cyclohexane and bromine water light and no light.

Alkenes CnH2n and Alkynes CnH2n-2

Alkenes and alkynes are classified as unsaturated hydrocarbons because they do not contain the maximum number of hydrogens.

Nomenclature of Alkenes and Alkynes

To name an alkene name the position of the double bond in the carbon chain and change the ane to ene.

To name an alkyne the position of the triple bond in the carbon chain and change the ane to yne.

Reactions of Alkenes and Alkynes

Alkenes and Alkynes undergo hydrogenation.

CH=CH + H2 --Pt--> CH2=CH2

CH2=CH2 + H2 --Pt--> CH3CH3

Alkenes and Alkynes undergo halogenation.

CH=CH + Br2 ----> CHBr=CHBr

CH2=CH2 + Cl2 ----> CH2ClCH2Cl

Alkenes and Alkynes undergo hydrohalogenation.

CH=CH + HCl ----> CH2=CHCl

CH2=CH2 + HCl ----> CH3CH2Cl

 

 

 

Aromatic Compounds

Aromatic compounds are those compounds that have properties resembling benzene (C6H6). Although they have many double bonds, they do not react as do alkenes.

Nomenclature of Aromatics

Monosubstituted Benzenes

Name the substituent group followed by the word benzene. Some monosubstituted benzenes have special names. ie. methylbenzene = toluene

hydroxybenzene = phenol

analine

benzoic acid

benzaldehyde

When benzene is a substituent group (C6H5-) on another molecule it is named phenyl.

 

Disubstituted Benzene

Ortho means the two substituents are adjacent to eachother.

Meta means the two substituents are separated by one carbon.

Para means the two substituents are separated by two carbons.

Some disubstituted benzenes have special names such as xylene and come in three varieties: ortho-xylene, meta-xylene, para-xylene

Polysubstituted Benzenes

The benzene ring is numbered giving the lowest number to the functional group which gives may give the benzene a special name.

Alcohols

Alcohols have the -OH group.

Alcohol Nomenclature

Give the position of the -OH group on the carbon chain and change the ane ending to -ol

 

 

 

 

Reactions of Alcohols

Mild oxidation of primary alcohols gives aldehydes which can in turn be oxidized to acids.

CH3CH2OH --K2Cr2O7--> CH3CHO --K2Cr2O7--> CH3CO2H

Oxidation of secondary alcohols gives ketones.

CH3CHOHCH3 --KMnO4--> CH3COCH3

Alcohols react with active metals to form organometallic compounds and hydrogen much like the reaction between water and active metals.

2CH3CH2OH + 2Na ---> 2 CH3CH2ONa + H2

Ethers R-0-R'

Ethers are relatively unreactive.

Naming Ethers

The name of each substituent group followed by the word ether. (Not IUPAC)

Aldehydes RCHO

Aldehydes are given the name of the hydrocarbon changing the -ane ending to -al.

Ketones RCOR'

Ketones are named by giving the location of the oxygen on the carbon chain and changing the -ane ending to -one

Reaction of Aldehydes and Ketones

Aldehydes react with silver ion to form an acid ion and metallic silver.

Aldehydes and ketones react with hydrogen in the presence of Ni or Pt to form alcohols.

Organic Acids RCO2H and Esters RCO2R'

Organic acids tend to be weak acids but will react with strong bases.

Organic acids react with alcohols to form esters.

Polymers

The term polymer means many unit. There are many kinds of polymers each with its own properties and uses.

Demo:

Polymeric Balls

Demo:

Nylon 6-6