organic (short 15).notebook · organic (short 15).notebook 1 june 04, 2015 part i hydrocarbons...

Organic (Short 15).notebook

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June 04, 2015

Part I Hydrocarbons

Organic chemistry is the study of carbon compounds. Most chemists in the world are employed as organic chemists. There are over 2 million organic compounds in existence with thousands of new ones being synthesized every year. Inorganic compounds, in contrast, number around 50 thousand. Why so many organic compounds? This comes from the carbon atom’s ability to bond with itself to form long chain and branched chain structures as well as cyclic structures. Organic compounds are molecular (covalent bonding between atoms) and exhibit the following properties:

1. They are generally nonpolar and thus insoluble in water.2. They are nonelectrolytes (except for weak organic acids)3. They have weak intermolecular forces of attraction – van der Waals forces and thus low melting points.4. The mechanisms of organic reactions generally involve high activation energies and thus organic compounds show reactivity 5. (compared to inorganic compounds).

Recall from you study of bonding that the carbon atom undergoes sp3 hybridization when bonding (forming four equivalent hybrid orbitals) and forms a tetrahedral structure when bonding with four other elements. Carbon atoms can also share two pairs of electrons (double bond) and three pairs of electrons (triple bond). When drawing the structural formulas or organic compounds keep in mind the number of shared pairs (dashes) atoms can have:

Carbon : 4 Nitrogen: 3Hydrogen: 1 Halogens: 1Oxygen: 2

The organic compounds that we will be studying can be divided into two broad categories: aliphatic and aromatic hydrocarbons (and their derivatives) and functional groups. We will name organic compounds using IUPAC (International Union of Pure and Applied Chemists) rules. In general, the first part of a name (prefix) tells us the number of carbon atoms while the second part of the name (suffix) tells us the classification. You will need to memorize the following prefixes:

Prefix # C atoms Prefix # C atoms

meth 1 hex 6eth 2 hept 7prop 3 oct 8but 4 non 9pent 5 dec 10


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Aliphatic Hydrocarbons (aliphatic means straightchain or branched structures)

Alkane family

– general formula is CnH2n+2

– all C to C bonds are single bonds; this is known as a saturated compound– suffix is “ane”– as you increase in molecular mass within the family the van der Waals forces increase and the melting and boiling points increase

draw methane, CH4

draw pentane:

note: as molecular weight of alkanes increases, VDW forces increase and boiling point increases (gasàliquidàsolid)

Fossil fuels are mostly aliphatic hydrocarbons derived from the decomposition of onceliving organisms. The energy provided by these compounds originally came from the sun. Petroleum is a mixture of fossil fuel hydrocarbons containing from 5 to 25 carbon atoms. Natural gas, which is usually associated with petroleum deposits, consists mostly of methane but also contains significant amounts of ethane, propane and butane.

The components of petroleum are separated on the basis of difference in boiling points by a process called fractional distillation. The 5 carbon to 12 carbon components make up the gasolines. Additional gasoline can be produced by breaking apart longer chain carbon molecules to smaller molecules in a process called pyrolytic cracking.

Alkene Family

– general formula is CnH2n

– contain one C to C double bond; therefore unsaturated– suffix is “ene”

Draw ethene, C2H4

draw 2hexene

Alkyne Family

– general formula is CnH2n2

– contain one C to C triple bond; therefore unsaturated– suffix is “yne”

1st member: ethyne, C2H2 (also known as acetylene)

2nd member: propyne, C3H4

Note: Isomers are compounds having the same chemical formula but different structural formulas. The greater the number of carbon atoms in a molecule, the greater the number of possible isomers.

Draw and name two isomers of pentane:

Substitution/Addition Groups:

halogens: alkyl groups: others:

F fluoro CH3 methyl NO2 nitroCl chloro C2H5 ethylBr bromo C3H7 propylI iodo


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June 04, 2015

Practice Problems – Writing Structural formulas for hydrocarbons and their derivatives

1. ethane:

2. 1,1dibromopropane:

3. 3methylpentane:

4. chloroethane:

5. 1,2dichloropropane:

6. trichloromethane:

7. 1chloro4methylhexane:


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June 04, 2015

Part II Functional Groups

Alcohols

The functional group is called the hydroxyl group and has the formula –OH.

Monohydroxy alcohols:

» contain one hydroxyl group» suffix is “ol”» if carbon atom having the –OH group is bonded to one other carbon the alcohol is classified as primary» if carbon atom having the –OH group is bonded to two other carbon atoms the alcohol is classified as secondary» if carbon atom having the –OH group is bonded to three other carbon atoms the alcohol is classified as tertiary

Examples:

Dihydroxy Alcohols

» contain two hydroxyl groups» suffix is “diol”» known as glycols

Example:

Trihydroxy Alcohols

> three hydroxyl groups> suffix is “triol”

Example:


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June 04, 2015

Acids

– The functional group is called the carboxyl group and has the chemical formula COOH and the structural formula:

– This functional group always appears at the end of the molecule– In name acids drop the “e” from the alkane and add the suffix “oic” acid

Examples:

methanoic acid (formic acid):

ethanoic acid (acetic acid):

Aldehydes

» Functional group is the aldehyde group which has the chemical formula –CHO and the structural formula:» Always occurs at the end of the molecule» In naming aldehydes drop the “e” from the alkane and add the suffix “al”» Aldehydes are the products of the oxidation of primary alcohols

Examples:

Methanal:

Propanal:

Ketones

» The functional group is the carbonyl group having the chemical formula –CO and the structural formula» Ketones are made by oxidizing secondary alcohols» Ketones are named by droping the “e” from the alkane and adding the suffix “one”

Examples:

Propanone (also called acetone – the main ingredient in nail polish remover):

2pentanone:


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June 04, 2015

Ethers

» The functional group is the ether group having the chemical formula ROR (R = alkyl group, i.e. methyl. Ethyl., etc)» In naming ethers we name the alkyl group on the left of the oxygen followed by the alkyl group on the right and the word “ether”

Examples:

dimethyl ether:

ethyl butyl ether:

diethyl ether:

Amines

• The functional group is the amine group with the chemical formula N –• In naming we use the suffix “amine”

Examples: methylamine

2butanamine

Amide O R’

• The functional group is the amide, R –C – N – H• In naming we use the suffix “amide”

Examples: ethaneamide


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June 04, 2015

Practice Problems – Writing Structural Formulas for Organic Compounds That Contain Functional Groups1. ethanol: 7. propanamine:

2. butanoic acid: 8. ethyl butyl ether:

3. 3heptanone: 9. pentanal:

4. 1,3propanediol: 10. propanamide:

5. 3methylpentanoic acid: 11. 1,2,3propanetriol:

6. diethyl ether: 12. 2propanol:


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June 04, 2015

Part III Organic Reactions

Recall that organic reactions typically proceed at much slower rates than do inorganic reactions. For this reason, the use of catalysts is a common practice. In many organic reactions, only the functional group is involved. The greater part of the reacting molecules remains unchanged during the course of the reaction, and can easily be identified in the products.

Oxidation

Saturated hydrocarbons react readily with oxygen under conditions of combustion. Such reactions result in the oxidation of the carbon to carbon monoxide or carbon dioxide, depending on the amount of oxygen available. Hydrocarbons react with oxygen gas in a complete combustion to produce carbon dioxide gas and water vapor:

CH4(g) + 2O2(g) à CO2(g) = 2H2O(g)Complete combustion occurs when the carbon in the hydrocarbon is oxidized to its highest state, +4, producing CO2.

Incomplete combustion takes place at relatively low temperatures and in limited amounts of oxygen gas. In this case the carbon is oxidized to a lower state such as +2 (as in CO) or 0 (as in C). the reaction can be written as:

CH4(g) + O2(g) à CO(g) + H2O(g) + C(s)The oxygen is reduced to water as well as the oxide of carbon. Oxidation reactions have great significance because of the liberation of energy associated with them. Energy is derived from fuels by combustion and from food by cellular respiration, both processes involving oxidation reactions.


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Substitution

As the name implies, substitution reactions involve replacing one kind of atom or group with another kind of atom or group. For the saturated hydrocarbons, all substitution reactions (except for the special cases of combustion and thermal decomposition) involve replacement of hydrogen atoms. The halogen (F, Cl, Br, I) derivatives of the alkanes can be prepared by substitution reactions between the alkane and the halogen. The general term for these reactions is halogen substitution. Saturated hydrocarbons typically undergo substitution reactions. Preparation of the halogen derivatives by substitution always results in a byproduct of the halogen acid.

example: ethane + chlorine à

Addition

Addition reactions involve adding one or more atoms to carbon atoms that are attached to other carbon atoms by double or triple bonds. Thus, addition reactions are generally limited to the unsaturated hydrocarbons. In these reactions we add across the double (or triple) bond and thus saturate the hydrocarbon. Addition reactions take place more easily than substitution reactions. Their rates are often as great as those of ionic reactions. As a result, unsaturated compounds are considered more reactive than saturated compounds. Furthermore, those with triple bonds (alkynes) tend to be more reactive than those with double bonds (alkenes). Addition of hydrogen to an unsaturated hydrocarbon, however, usually requires the presence of a catalyst and an elevated temperature. The hydrogen addition reaction is called hydrogenation. Addition reactions between unsaturated hydrocarbons and chlorine and bromine to produce halogen derivatives take place at room temperature.

example: propene + bromine à

Addition reactions are characterized by the formation of a single product. This is in contrast with substitution reactions in which more than one product is typical.


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Fermentation

Fermentation is a process ordinarily associated with living systems. Enzymes produced by the organisms serve as catalysts for the reactions in which organic molecules are broken down. In fermentation a sugar (glucose) is converted to ethanol and carbon dioxide in the presence of the yeast enzyme zymase:

C6H12O6 à C2H5OH + CO2

Esterification

Esterification derives its name from the name of the products, esters. Esterification involves the reaction between an organic acid and an alcohol to produce an ester and water. Since esterification involves an acid and an OH group, it is often compared with neutralization of inorganic acids and bases, producing salts and water. Esterification, however, is not an ionic reaction, and esters are covalent compounds. Esterification is a slow reaction, usually requiring a catalyst, and it is reversible. Esters are responsible for the aromas associated with many fruits, flowers, and leaves. Lipids, (fats and oils) are esters formed from esterification of glycerol (1, 2, 3 propantriol) by longchain organic acids (fatty acids). The name of an ester is taken from the alcohol (“yl” suffix) and acid (“oate” suffix) from which it was made.

example: propanoic acid + ethanol à

Note: concentrated sulfuric acid is added to the reaction mixture to keep the equilibrium shifted right via LeChatelier (because H2SO4 is a good water absorber).


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example: 3 fatty acids + glyceroal à ester + H2O

C17H35COOH HOCH2 C17H35COOCH2

C17H35COOH HOCH à C17H35COOCH + 3H2O

C17H35COOH HOCH2 C17H35COOCH2

stearic acid glycerol glyceryl stearate

Saponification

Saponification refers to the hydrolysis of a fat (an ester of glycerol and fatty acids) in the presence of a base. The products are glycerol and soap, which is the salt of a fatty acid.

example:

C17H35COOCH2

C17H35COOCH2 + 3NaOH à 3 C17H35COONa+ + C3H5(OH)3

C17H35COOCH2

glyceryl stearate sodium stearate glycerol (a soap)


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June 04, 2015

Polymerization

Polymerization is a name given to reactions in which large molecules are made from smaller molecules. Polymerization occurs in nature in the production of proteins and starches by living organisms. Synthetic rubbers, plastics, and fibers are results of polymerization reactions.

Polymers are composed of many repeating units, called monomers which are joined together by one of two types of polymerization reactions condensation or addition.

Condensation Polymerization

Condensation polymerization results from joining monomers by a process called dehydration synthesis. This process may be repeated to produce a longchain polymer. Monomers involved in condensation must have at least two functional groups. Examples of condensation polymers include silicones, polyesters, polyamides, phenolic plastics, and nylons. The example below is an example of a reaction between a carboxylic acid and an amine to produce an amide. Polyamides are polymers in which the carboxylic acid and amine monomer units are linked by amide bonds. Many types of nylon are polyamides.

O H O H

R – C – OH + H – N – R à R – C – N – R + HOH

carboxylic acid + amine à amide + water

Proteins are polymers made by the dehydration synthesis of amino acids. This is another example of condensation polymerization.

Example:

H H O H CH3 O H H O H CH3 O

H N – C – C + H N – C – C à H N C – C – N – C C

H OH H OH H H OH

glycine alanineO

+ H H

Addition Polymerization

Addition polymerization, as do all addition reactions, involves opening of double and triple bonds of unsaturated hydrocarbons. Vinyl plastics, such as polyethylene and polystyrene, are examples of addition polymerization.

H H x C C à H(CH2CH2)xH H H example: ethylene (ethene) à polyethylene


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June 04, 2015

organic (short 15).notebook · organic (short 15).notebook 1 june 04, 2015 part i hydrocarbons...

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