ORGANIC CHEMISTRY

What is Organic Chemistry?

The terms organic and inorganic are used to distinguish between two different groups of substances. Organic chemistry is the study of all carbon compounds (except oxides of carbon, carbonates, carbides and cyanides).

These exceptions plus the substances of the remaining elements are considered to be inorganic.

differences between organic and inorganic compounds.

How Important is Organic Chemistry?

Organic chemistry involves the study of organic substances, which include those derived from living organisms as well as numerous synthetic substances. Examples of orgnaic materials are:

list of different organic materials

Origin of Organic Substances

Although organic compounds may be synthesized from inorganic materials

it is generally more economical to extract them from organic sources:

- living and dead plants and animals

- coal (decaying plant material)

- natural gas products of decayed

marine plants and animals

- petroleum

Very nearly all orgnanic compounds are derived from hydrocarbons (compounds that contain only hydrogen and carbon). The main source of hydrocarbons is petroleum.

Petroleum (crude oil) is found in the earth's crust as a black, sticky liquid. This crude oil is a mixture of gases, liquids and solids which can be separated into hundreds of individually useful hydrocarbon compounds.

diagram of petroleum in earth's crust

The process in which petroleum is separated into its useful components and then purified is called PETROLEUM REFINING.

Since crude petroleum is a complex mixture of hydrocarbons, it has no fixed boiling point. The mixture has a boiling or distillation range which may start as low as 20^oC and end above 400^oC. The difference in the volatility (as indicated by boiling point) of components (fractions) in the mixture makes possible the initial rough separation of crude petroleum by fractional distillation (fractionation). In general, the smaller the molecule, the lower it's boiling point. As a result, fractional distillation sorts the crude petroleum into it's main constituents according to the size of the molecules.

The separation of crude petroleum by fractional distillation is acheived in a bubble tower which houses vertical columns containing series of horizontal plates or trays. The crude oil is heated to about 400^oC and the vapours pass into the fractionation tower (as shown below).

Why Are There So Many Organic Compounds?

There are over 6 million different organic compounds and there are only about 250,000 inorganic compounds. Obviously the organic far outnumber the inorganic. So you may be asking yourself the question "How can there be so many organic compounds?" After all organic compounds are made up primarily of carbon, hydrogen and a few other elements, whereas inorganic compounds are made up of combinations of the remaining 100 or so remaining elements.

The answer lies in the ability of the carbon atom to combine with itself. The process of bonding identical atoms is called catenation. Other atoms, such as B, Si, and P, are capable of catenation but only carbon atoms form strong covalent bonds. This unusual ability enables carbon atoms to form all kinds of short chains, long chains, branching chains, rings, rings attached to chains, etc. In addition, the bonds between the carbon atoms may be single, double, or triple. These facts together make the number of potential organic compounds almost infinite.

Classification of Organic Compounds

Since there is such a vast number of known organic compounds, if we want to study them it is necessary to classify them into major groups. As mentioned earlier nearly all organic compounds can be regarded as being derived from the very large number of different hydrocarbons (contain only hydrogen and carbon). The following is a classification scheme for organic compounds based on molecular structure.

diagram of classification

ALKANES

Alkanes are aliphatic, saturated hydrocarbons. The term "aliphatic" refers to compounds that have a chain structure. The term "saturated" means that all the carbon-carbon bonds are single bonds.

The the general molecular formula for an alkane is C_nH_2n+2, where n is the number of carbon atoms.

The simplest alkane is methane (n=1), which has the molecular formula CH₄. Methane is the major constituent of natural gas. Ethane, C₂H₆, is a minor constituent of natural gas. Propane, C₃H₈, and butane, C₄H₁₀ are used as fuels. The structural formulas for each of these alkanes are shown below:

Methane Ethane Propane Butane

Physical Properties

State: The alkanes up to butane are all gases (at room temperature). The higher members are liquids and solids.

Melting/boiling points: The melting points and boiling points of the alkanes increase with increasing molecular size.

Solubility: The bonds are essentially non-polar so the molecules are essentially non-polar. This means that they do not dissolve in water.

Electrical Conductivity: The fact that there are no free electrons accounts for the observation that they do not conduct electricity.

Naming Straight Chain Alkanes Alkanes are named using prefixes to denote the number of carbon atoms present and adding the ending -ane. The following is a list of the prefixes for the first 10 alkanes:

meth - 1 C atom hex - 6 C atoms

eth - 2 C atoms hept - 7 C atoms

prop - 3 C atoms oct - 8 C atoms

but - 4 C atoms non - 9 C atoms

pent - 5 C atoms dec - 10 C atoms

IUPAC Nomenclature for Branched Chain Alkanes

Although the rules for naming organic compounds have been set up by the International Union of Pure and Applied Chemistry (IUPAC) no one follows the rules completely. Many compounds have commonly used names that do not conform to IUPAC rules. For example, "ethanoic acid", CH₃COOH, is the IUPAC name for "acetic acid." You are even more familiar with the name of its dilute aqueous solution - vinegar. Also, as the names become more complex, chemists tend to simplify them: alloxanic acid is much easier than its IUPAC name:

tetrahydro-4-hydroxy-2,5-diketo-4-imidazole-carboxylic acid

Despite the fact that IUPAC is not always strictly adhered to it is a very important system. With all of the 6 million different organic substances there must be one accepted method amongst chemists in order to name and identify them. We will investigate the naming of hydrocarbons. The naming of hydrocarbons is of particular importance because their names form the basis of naming all other organic compounds.

We have already discussed the naming of straight chain alkanes (all carbon atoms in the chain are linked to no more than two other carbon atoms).

The next step involves naming branched chain alkanes (if one or more carbon atoms are linked to more than two other carbon atoms). For example:

butane 2-methylpropane

These branches are referred to as "side chains" or "substituents."

Naming Substituents For now, we will simplify things by limiting our discussion of branches to alkyl groups (C_nH_2n+1 groups). Alkyl groups are formed by removing one H atom from the alkane. The resulting group then has the ability of making another covalent bond. To name the alkyl groups simply drop the "-ane" suffix and add "-yl". For example:

Alkyl Groups

Name	Molecular Formula	Name	Molecular Formula
methyl	-CH₃	isobutyl	CH₃CHCH₂CH₃
ethyl	-CH₂CH₃	n-pentyl	-CH₂CH₂CH₂CH₂CH₃
n-propyl	-CH₂CH₂CH₃	n-hexyl	-CH₂CH₂CH₂CH₂CH_2CH3
isopropyl	CH₃CHCH₃	n-heptyl	-CH₂CH₂CH₂CH₂CH₂CH₂CH₃
n-butyl	-CH₂CH₂CH₂CH₃	n-octyl	-CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₃

Naming Branched Chain Alkanes

Example: What would be the proper IUPAC name for the following compound?

There are rules for naming an alkane:

1. Determine the longest continuous chain of carbon atoms in the molecule

and name it. This is the parent stem.

2. Number the carbon atoms of the continuous chain consecutively starting at the end closest to the branching (this will ensure that the substituents are assigned the lowest possible numbers).

3. Locate the branch by the number of the carbon atom to which it is attached on the continuous chain.

4. Name the branch.

5. Write the name of the alkane by first arranging all the substituents in alphabetical order (each preceded by the number of the carbon to which they are attached) and then add the name of the parent stem. If there are two or more identical substituents, the prefixes di-, tri-, tetra-,

penta-, etc are used. Numbers are separated from numbers by comas and numbers are separated from names by hyphens.

ALKENES

Alkenes are aliphatic hydrocarbons, but unlike alkanes they are unsaturated. This means that these type of hydrocarbons contain atleast one carbon-carbon double bond. Alkenes have the general molecular formula C_nH_2n, where n is the number of carbon atoms (Note: there is no n = 1 member).

The simplest alkene is ethene, C₂H₄, which has the following structural formula:

ethene

The common name for ethene is ethylene. Do you know the significance of this compound? It is from this substance that chemists make polyethylene, a plastic used for containers, packaging, electrical insulation, etc.

Physical Properties Alkenes have very similar properties to alkanes. like alkane molecules, alkenes are essentially non-polar and thus insoluble in water and other polar solvents. However, alkenes do dissolve in other liquid hydrocarbons (like dissolves like). The lighter alkenes are gases at room temperature while the heavier alkenes are liquids and solids with low melting points.

IUPAC Nomenclature of Alkenes

The IUPAC system of nomenclature for the alkanes applies to the alkenes with the following additions:

1. Determine the longest continuous chain of carbon atoms containing the double bond. This is the parent stem.

2. The ending "-ene" is used (instead of "-ane") to idicate the presence of one carbon-carbon double bond.

3. The longest continuous chain is numbered so that the carbon atoms of the double bond have the lowest possible numbers, and next so that the branches have the lowest possible numbers.

The simplest type of alkenes are the straight chain compounds with only one double bond. Examples are shown below:

CH₂==CH₂ CH₂==CH--CH₃

ethene propene

CH₂==CH--CH₂--CH₃ CH₃--CH==CH--CH₃

1-butene 2-butene

Branched alkenes are not that difficult to name either (as long as rule #3 is remembered)

Examples: Provide the name for the following branched alkenes.

1. CH₃--CH₂--CH₂--C==CH₂ 2. CH₃--CH₂--C==CH₂

CH₂--CH₃ CH₃

_________________________ _________________________

3. CH₃ 4. CH₃

CH₂==CH--C--CH₂--CH₃ CH₃--C==CH--CH--CH₂--CH₃

CH₃ CH₂--CH₃

_________________________ _________________________

There are also cases where more than one double bond is present. If a compound contains two carbon-carbon double bonds (diene), then the name ends with "-adiene". If the compound contains three carbon-carbon double bonds (triene), then the name ends with "-atriene". In each case the location of the double bonds must be indicated with numbers.

Examples: Name the following two alkenes.

H H H H H H H H H H

C==C--C==C C==C--C==C--C==C

H H H H

1,3 - butadiene 1,3,5 - hexatriene

Note: these compounds do not follow the general molecular formula, C_nH_2n.

Isomerism Among the Alkenes

Isomers exist among alkenes because there is no free rotation about a double bond (this is obvious if a molecular model is used to make an alkene).

In order for rotation to occur about a double bond, one of the two bonds in the double bond would have to be broken, which requires a considerable amount of energy.

For example, consider two different alkenes with the molecular formula C₄H₈.

CH₃ H CH₃ CH₃

C == C C == C

H CH₃ H H

__________________ __________________

These two isomers have the same structural framework (all atoms are connected in the same way) but different arrangements of atoms in space (geometries). Thus, these types of isomers are called geometric isomers.

To distinguish between two geometric isomers, chemists use the terms "cis" and "trans". Trans means across (as in transatlantic). In the above examples the first isomer has the CH₃ groups across from each other. This is the trans isomer. In the second isomer the CH₃ groups are on the same side of the double bond. This is the cis isomer.

Note: Cis and trans isomers can not exist if one carbon of the double bond bears two identical groups.

Example: Propene

There can never exist cis and trans isomers of propene since one of the carbons at the double bond holds two hydrogen atoms.

When naming geometric isomers of alkenes all the IUPAC rules discussed above still apply. The only difference is that the term cis or trans is put in front of the name to idicate the arrangement of the identical substituents about the double bond.

Examples: 1. Name the two geometric isomers above.

2. CH₃ CH₃

C == C _____________________

CH₃--CH₂ H

3. CH₃

CH₃ CH--CH₃

C == C ________________________

H H

ALKYNES

Alkynes are aliphatic hydrocarbons and like alkenes, they are unsaturated. However, these type of compounds contain atleast one carbon-carbon triple bond. Alkynes have the general molecular formula C_nH_2n-2, where n is the number of carbon atoms (once again there is no n = 1 member).

The simplest alkyne is ethyne, C₂H₂, which has the following structural formula:

ethyne

The common name for ethyne is acetylene. Do you know the significance of this compound?

A major use for acetylene is in the oxy-acetylene torch for cutting and welding metals.

Physical Properties Alkynes have very similar properties to alkenes and alkanes. Alkynes are essentially non-polar and thus insoluble in water and other polar solvents. Again, alkynes are gases, liquids or low melting solids at room temperature.

IUPAC Nomenclature for Naming Alkynes The IUPAC nomenclature for the alkynes is identical to that of the alkenes except the ending "-yne" replaces the ending "-ene" to indicate the presence of one triple carbon-carbon bond. Once again the position of the triple bond must be indicated by the lowest possible number.

Examples:

H--C==C--H H--C==C--CH₃

ethyne (acetylene) propyne

H--C==C--CH₂--CH₃ CH₃--C==C--CH₃

1 - butyne 2 - butyne

Provide the name for the following alkynes:

1. CH₃ 2. CH₃--C==C--CH--CH₃

CH==C--CH--CH₃ CH₂--CH₃

_________________________ ____________________________

Write the structural formula for the following compounds:

1. 4,4-diethyl-1-hexyne 2. 5-ethyl-4-propyl-2-heptyne

Haloalkanes (Alkyl Halides) Alkyl halides are hydrocarbon derivatives. That is they have the general molecular formula

R--X, where X represents a halide (such as F, Cl, Br, or I) and R represents any organic substituent. The alkyl group may contain single, double, or triple carbon-carbon bonds, however, alkane (single carbon-carbon bonds) are the most popular. Alkyl halides are made during a process called halogenation (to be discussed later). During halogenation one or more hydrogen atoms of a hydrocarbon are replaced with halogen atoms.

Physical Properties: Generally, alkyl halides are relatively non-polar substances with little solubility in water. Their biological effects are pronounced and seem to follow a general pattern. Depending on the particular halogen compound and its concentration it may change the activity of cells, especially nerve cells (ie. DDT, hexachlorocyclohexane)

Nomenclature of Alkyl Halides: In the sytematic (IUPAC) nomenclature, the halogen is treated as a substituent to the alkane framework. The same rules apply only the prefix fluoro, chloro, bromo, or iodo is added to the name of the parent hydrocarbon stem. The number of added halide atoms is indicated by an appropriate prefix (ie. di, tri, tetra, etc). Note the following rules and examples:

1. Determine the longest continuous carbon chain and name it. This is the parent stem.

2. List all the substituents as prefixes in alphabetical order.

3. Use the lowest set of numbers to indicate the positions of the substituents.

Examples: Cl

Cl C H ______________________________

Cl H

Cl C C H ______________________________

Cl H

Note: For identical sets of numbers choose the set of numbers which yields the lowest number to the first substituent listed in the name.

Ex. CH₂ CH₂

Cl Br

1-bromo-2-chloroethane NOT 2-bromo-1-chloroethane

F F

C C ______________________________

F F

H CH₃ H CH₃ H H

C C C C C C H ______________________________

H I H H H

H H H Cl Cl

H C C C C C C H ______________________________

H H H H H

Cyclic Hydrocarbons In some hydrocarbons, the ends of the carbon chain bond together, forming a ring. The resulting molecules may be:

1. cycloalkanes

2. cycloalkenes

3. cycloalkynes

Cycloalkanes The general molecular formula for a cycloalkane is C_nH_2n (the same as the general formula for alkenes. In fact cycloalkanes are isomers of alkenes). For convenience cycloalkanes can be represented by simple geometric figures. The system for naming memebers of this class fo compounds is straightforward. Alkane names are preceeded by the prefix "cyclo-". For example:

cyclopropane cyclobutane cyclopentane cyclohexane

Cycloalkanes can also have substituent groups attached to the ring. In this case naming a substituted cyclic alkane requires numbering of the individual ring carbons only if more than one substituent is attached to the ring. For example:

It should be noted that in cyclic compounds rotation about a single carbon-carbon bond is not possible. Thus, two geometric isomers (stereoisomers) are possible. Again, the terms cis and trans are used to indicate the isomer.

Cycloalkenes Alkenes consisting of a closed ring structure are known as cycloalkenes. Cycloalkenes have the general molecular formula C_nH_2n-2 (the same as for alkynes. Cycloalkenes are isomers of alkynes).

As with cycloalkanes, the stem name for cyclic alkenes is the same as that for the corresponding straight chain alkenes. The name for the cycloalkene is preceeded by the prefix "cyclo-". However, in this case the suffix "-ene" replaces "-ane" to indicate the presence of a double bond. For example:

cyclobutene cyclohexene 1,3-cyclohexadiene

Like cycloalkanes, the cycloalkenes may be substituted. the substituents must be numbered such that they are the lowest possible numbers. Once again, geometric isomers are possible and cis and trans are used to distinguish between the two.

diagram of cis and trans cycloalkenes

Cycloalkynes Cycloalkynes have the general molecular formula C_nH_2n-4. The same rules as described for naming cycloalkenes apply to cycloalkynes. The only difference is the suffix "-ene" is changed to "-yne" to indicate the presence of a triple bond. For example:

cyclohexyne cycloheptyne cyclooctyne

Functional Groups By definition a functional group is an atom or group of atoms (a unit of structure) within a molecule which is responsible for the characteristic chemical properties of a compound. It is a structural feature that identifies a family of compounds and gives its members a common property. For example: consider the four alcohols below:

CH₃OH CH₃CH₂OH CH₃CH₂CH₂OH CH₃CHCH₃

These compounds have different hydrocarbon skeletons but the same functional group, -OH. Therefore, the general formula for an alcohol is

R--OH, with R representing the hydrocarbon portion of the molecule.

Note: while reactions are occuring at a functional group the rest of the molecule, the skeleton, survives unchanged.

In the sections that follow we shall briefly examine other common families of compounds such as alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, and amines.

Alcohols If one of the hydrogen atoms in a hydrocarbon is replaced by a hydroxyl group, -OH, an alcohol results. The alcohols are derived from the alkanes, and have the general molecular formula C_nH_2n+1OH (or R-OH).

Examples:

H H H H H H

H--C--H ------> H--C--OH H--C--C--H ------> H--C--C--OH

H H H H H H

methane methanol ethane ethanol

Methanol, CH₃OH, is the simplest alcohol. It is also very poisonous. This compound is known as wood alcohol because it can be obtained by heating wood in the presence of air. A word of warning about methanol: death can result from drinking 30 mL and permanent blindness from lesser amounts.

Methanol is used in windshield washer fluid, and is used to manufacture many other substances including plastics, fertilizers, and pharmaceuticals.

Ethanol, CH₃CH₂OH, is the alcohol present in beer, wine, and liquor. Ethanol is formed during the fermentation process which involves the breakdown of sugar (glucose)

yeast

C₆H₁₂O₆ -------> 2CH₃CH₂OH + 2CO₂

glucose ethanol

Isopropyl alcohol is most familiar as the compound in rubbing alcohol. This is also an extremely poisonous alcohol.

Physical Properties

State: Under normal conditions methanol, ethanol, and other alcohols containing up to about twelve carbon atoms are liquids.

Boiling Points: The boiling points increase with increases in the number of carbon atoms. The boiling points of the alcohols are substantially greater than the boiling points of the related alkanes.

ALKANE	BOILING POINT	ALCOHOL	BOILING POINT
Methane	- 164^oC	Methanol	65^oC
Ethane	- 89^oC	Ethanol	78.5^oC
Propane	- 42^oC	Propanol	97.4^oC
Butane	- 0.5^oC	Butanol	117^oC

The difference in boiling points can be directly attributed to the presence of the hydroxyl group. The reason that the boiling points are so much higher is due to the increased forces of attraction between molecules, due to hydrogen bonding.

hydrogen bonding diagram

Solubility: The lighter alcohols are totally soluble in water due to the presence of the hydroxyl group which allows hydrogen bonding with the water molecules. However, as the number of carbon atoms increase the solublity decreases.

Chemical Properties The reactions of alcohols are extensive and varied. Thus, we will limit our discussion to one type of reaction - esterification. This will be discussed after carboxylic acids have been introduced.

Types of Alcohols There are three types of alcohols based on the position of the hydroxyl group in the molecule:

i. primary

ii. secondary

iii. tertiary

Ethers Members of this group of compounds have an oxygen atom bridging two alkyl groups, R and R'. The general formula is therefore:

R--O--R'

Ethers are isomeric with alcohols, but on the other hand, the properties of ethers are very different from the properties of alcohols (see below).

Diethyl ether, CH₃CH₂OCH₂CH₃, is the most common ether. It is used industrially as a solvent and, at one time, medically as an anesthetic. Due to the fact that it is very flammable and must be used with caution it has been replaced with other safer compounds.

Nomenclature for Ethers The common name of an ether is determined by noting the name of the groups attached to the oxygen atom, followed by the word "ether". Examples:

CH₃--O--CH₂CH₃ ethylmethyl ether

CH₃--O--CH₃ dimethyl ether (or just methyl ether)

CH₃CH₂--O--CH₂CH₃ diethyl ether (or just ethyl ether)

Name the following ether:

CH₃

CH₃--CH₂--CH₂--O--C--H ___________________________

CH₃

Physical Properties Although ethers are more polar than hydrocarbons, their boiling points are comparable (since no hydrogen bonding between ethers). There is also a noticeable difference between the boiling points of ethers and the isomeric alcohols.

Ether	Name	Boiling Point (^oC)	Alcohol	Boiling Point (^oC)
CH₃OCH₃	dimethyl ether	-23	CH₃CH₂OH	79
CH₃OCH₂CH₃	ethylmethyl ether	10.8	CH₃CH₂CH₂OH	97
CH₃CH₂OCH₂CH₃	diethyl ether	35	CH₃(CH₂)₃OH	117

The lower boiling points of the ethers can be attributed to the fact that there does not exist any hydrogen bonding among ethers whereas there does among alcohols.

Ethers are comparably soluble in water to the alcohols of similar molecular weight since they can form hydrogen bonds in water.

Carbonyl Group The carbonyl group has the following structure:

This is probably the most important functional group in organic chemistry. If one of the bonds from the carbon holds a hydrogen the compound is an aldehyde; if both of the bonds from the carbon hold organic groups the compound is a ketone.

Aldehydes The general formula for the aldehyde is:

R--C--H

Some examples of alsehydes are shown below:

O H O H CH₃

H C H H C C H H C C C H

H H H O

methanal ethanal 2-methylpropanal

The simplest aldehyde is methanal (formaldehyde). Methanal is a gas at room temperature but is also available as a 40% solutions in 5-12% methanol, called formalin. This solution is widely used as a disinfecting, sterilizing, and embalming agent. Large quantities of methanal are also used in the preparation of some plastics.

Preparation Aldehydes can be prepared by a number of different methods. The most common method used in laboratories is the oxidation of primary alcohols. The oxidation is carried out using an acidic solution of potassium permanganate, KMnO₄, or potassium dichromate, K₂Cr₂O₇, as oxidizing agents, which are reduced to Mn²⁺ and Cr³⁺, respectively. For example:

H H H O

K₂Cr₂O₇, H₃O⁺

H C C OH ---------------> H C C H + H₂

H H H

ethanol ethanal hydrogen

Nomenclature for Aldehydes The IUPAC system names an aldehyde by replacing the "-e" of the corresponding alkane with "- al". For example:

methanal ethanal propanal benzaldehyde

Ketones The members of this group have the general formula:

where R and R' represent alkyl

R C R' groups (not hydrogen)

Some examples of ketones are shown below:

H O H H H O H

H C C C H H C C C C H

H H H H H

propanone butanone

The simplest and best known ketone is propanone (acetone). it is a colourless liquid at room temperature and totally soluble in water. Large quantities are used industrially as a solvent and for producing other organic compounds. It is also found in paint removers and nail polish removers. Acetone is also biologically important. Abnormal metabolism in individuals causes the production of acetone; it is then excreted in the urine, or in severe cases even exhaled in the breath ("acetone breath").

Preparation Ketones can be prepared in the laboratory by the oxidation of secondary alcohols. The method of oxidation is similar to that described for aldehydes. For example:

H OH H H O H

K₂Cr₂O₇, H₃O⁺

H C C C H ---------------> H C C C H

H H H H H

2-propanol propanone

Nomenclature According to the IUPAC system, ketones are named by replacing the "-e" of the corresponding alkane with "-one". For example:

propanone 2-pentanone acetophenone

(dimethyl ketone) (methyl propyl ketone) (methyl phenyl ketone)

Physical Properties of Aldehydes and Ketones: Low molecular weith aldehydes and ketones are soluble in water due to the presence of the polar carbonyl group. Also aldehydes and ketones have higher boiling points than hydrocarbons of the same molecular weight. However, since aldehydes and ketones cannot form strong hydrogen bonds to each other, they have lower boiling points than corresponding alcohols.

CH₃CH₂CH₃ CH₃CH₂COH CH₃CCH₃ CH₃CH₂CH₂OH

propane propanal propanone propanol

bp -45^oC 49^oC 56^oC 97^oC

Carboxylic Acids Carboxylic acids (organic acids) are characterized by the functional group called the carboxyl group. The carboxyl group (-COOH) consists of a carbonyl group with a hydroxyl group attached to the carbon atom, as shown below:

Physical Properties Carboxylic acids are all weak acids. They are also polar substances. They can form strong hydrogen bonds with each other and with water. As a result, carboxylic acids generally have higher melting and boiling points than hydrocarbons, organic halides, or alcohols with the same number of carbon atoms (Note: the carboxyl group has two polar groups: carbonyl and hydroxyl).

CH₃CH₂CH₃ CH₃CH₂CH₂OH CH₃CH₂C--OH

propane propanol propanoic acid

bp -45^oC 97^oC 141^oC

Again due to the presence of the polar carboxyl group the low molecular weighth carboxylic acids show appreciable water solubility. However, as the size of the non polar portion increases the solubility decreases.

Preparation A general method for producing caboxylic acids in the laboratory is the oxidation of alcohols with an oxidizing agent such as potassium dichromate in acidic solution. Using a limited amount of oxidizing agent results in the aldehyde, whereas use of an excess of oxidizing agent yields the carboxylic acid. For example:

K₂Cr₂O7 (limited) CH₃C--H

H₃O⁺ ethanal

CH₃CH₂OH

ethanol

K₂Cr₂O₇ (excess) CH₃C--OH

H₃O⁺ ethanoic acid

Nomenclature for Carboxylic Acids Carboxylic acids are named in the IUPAC system by dropping the "-e" in the associated hydrocarbon and adding the suffix "-oic", followed by the word "acid" (Note: there also exist dicarboxylic acids. These are named as alkanedioic acids in the IUPAC system). For example:

organic acid chart from page H50

and carboxylic acids from page H51

Amines Amines and other nitrogen bearing compounds are among the most abundant organic molecules; they are, for example, components of the amino acids, peptides, proteins, and alkaloids (such as nicotine and caffeine). Many are medicinally active.

Amines are closely related to ammonia, NH₃, in structure and properties. As with alcohols, we can distinguish primary, secondary, and tertiary amines depending on the number of alkyl groups attached to the nitrogen atom. For example:

H R

NH3 R N N H R' N

H R'

R" ammonia

H CH₃ CH₃

CH₃ N N H

H CH₃ CH₃ N CH₃

methylamine dimethylamine trimethylamine

(primary amine) (secondary) (tertiary)

There are also aromatic amines, the

simplest of which is aminobenzene, C₆H₅NH₂,

commonly known as aniline.

Putrescine and cadaverine are two amines with very pungent odours. They are produced by decaying organisms. Such amines are called ptomaines and, in fact, can also be formed by the action of bacteria on meat and fish (thus the name ptomaine poisoning).

The compound (phenylisopropyl)amine (commonly known as amphetamine or benzedrine), acts as a stimulant to the central nervous system. It is used in nasal inhalers to relieve nasal congestion in people who have colds. This compound and others related to it are called "uppers" because of their ability to keep one active and awake. Unfortunately, they can cause drug dependence.

Below is a list of some other important amines and their uses.

Import. amines and uses, pg 525, Basic Concepts of Chemistry

Physical Properties Like ammonia most amines have unpleasant odours. The stench of decaying flesh is due to the amines putrescine and cadavarine (produced by the decomposition of proteins).

Amines are moderately polar substances and thus the simple amines are soluble in water (due to ability of the nitrogen atom to hydrogen bond). However, as the number of non-polar substituents increases the solubility decreases.

Like ammonia; amines are weak bases. They have boiling points higher than corresponding alkanes but, as expected, lower than alcohols.

CH₃CH₂CH₃ CH₃CH₂CH₂OH CH₃CH₂CH₂NH₂

propane propanol propylamine

bp -45^oC 97^oC 49^oC

Nomenclature for Amines Amines are named by adding "-amine" to the name of the alkyl group(s) attached to the nitrogen atom. For example, name the following amine.

CH₃ N __________________________

CH₂CH₃

CH_{3
N} __________________________

CH₂CH₃

CH₃ N __________________________

CH₂CH₃

Diamines There can also exist diamines. In this case the name "diamine" is added to the name of the alkyl group(s). It is also important in these type of compounds to indicate the position of the amino group. For example, name the following:

H₂NCH₂CH₂CH₂CH₂NH₂ _____________________________

(putrescine)

H₂NCH₂CH₂CH₂CH₂CH₂NH₂ _____________________________

(cadaverine)