Organic Chemistry

Selecting the parent chain

The first step in naming an alkane is to identify the longest chain, called the parent chain. If there is a competition between two chains of equal length, then choose the chain with the greater number of substituents

Isopropyl group

An alkyl group bearing three carbon atoms can only be branched in one way. (1-methylethyl)

Refining

A process that seperates petroleum into fuels and gasoline or oil. Gasoline represents only 19% of crude oil. Not satisfactory for current demand. Two processes are employed that increase the yield of gasoline from every barrel of crude oil.

If one substituent present

Assign to the lower possible number

For an alkane, the number of possible constitutional isomers increases with increasing molecular size.

Avoid drawing the same compound twice by IUPAC naming each compound.

Common names

So well entrenched that IUPAC allows them.

Cracking

The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.(thermal or catalytic cracking)

Reforming

The conversion of straight-chain hydrocarbons into branched-chain and cyclic hydrocarbons. Branched hydrocarbons and aromatic hydrocarbons show less of a tendency for knocking. It is therefore desirable to convert some petroleum into branched alkanes and aromatic compounds and then blend them with straight-chain alkanes. The combination of cracking and reforming effectively increases the gasoline yield from 19 to 47% for every barrel of crude oil. Gasoline is therefore a sophisticated blend of straight-chain alkanes, branched alkanes, and aromatic hydrocarbons.

IN 1892, a group of 34 European chemists met in Switzerland

and developed a system of organic nomenclature called the Geneva rules. The group ultimately became known as the International Union of Pure and Applied Chemistry or IUPAC. The original Geneva rules have regularly revised and updated.

Substituents

are branches connected to the parent chain

Alkyl groups bearing five carbon atoms can be branched in many more ways.

isopentyl or isoamyl(3-methylbutyl) neopentyl(2,2-dimethylpropyl)

Cyclo

term used to indicate the presence of a ring in the structure of an alkane(CYCLOALKANES) CYCLOPROPANE, CYCLOBUTANE, CYCLOPENTANE

nomenclature

the system of naming compounds

Hydrocarbons that lack pi bonds are

saturated hydrocarbons, or alkanes. names of these compounds usually end in with the suffix, -ane, eg. propane, butane, pentane

Alkyl groups bearing four carbon atoms can be branched three ways

sec-butyl(1-methylpropyl) isobutyl(2-methylpropyl) tert-butyl(1,1-dimethylethyl)

Naming bicyclic compounds

Compounds that contain two fused rings. Same four step procedure but with differences in naming and numbering the parent

Relative stability of Isomeric Alkanes

In order to compare stability of constitutional isomers, look at heat liberated when they undergo combustion.

Identifying constitutional isomers

Name each compound. Compare the names.

presence of substituent

Name parent compound by starting on the longest path that connects the two bridgeheads. Start at the first bridgehead going down on longest path then second longest path, then shortest path. the shortest path has the highest number

Naming Substituents

Once the parent has been identified, the next step is to list all of the substituents.. Substituents are named with the same terminology used for naming parents, only we add the suffix "yl" instead of "ane". These groups are generically called alkyl groups. When an alkyl group is connected to a ring, the ring is generally treated as the parent.. However, when the ring is comprised of fewer atoms than the rest of the structure, it is common practice to name the ring as a substituent ( cycloalkyl group)

Identify the bridgeheads

The two carbon atoms where the rings are fused together. Identify the paths connecting these two bridgeheads. order from largest to smallest and place in the middle of the parent, surrounded by brackets.

Multiple substituents present

assign numbers so that the first substituent receives the lower number. The first locant should be as low as possible. If there is a tie, the second locant should be as low as possible. If the previous rule does not break the tie, lowest number should be assigned alphabetically. Same rules apply for cycloalkanes. When a substituent appears more than once in a compound, a prefix is used to identify how many times that substituent appears in the compound(di=2, tre=3, tetra=4, penta=5, and hexa=6). Hyphen used to separate numbers from letters while commas used to separate numbers from eachother.

Change in Enthalpy (ΔH)

associated with the complete combustion of 1 mol of pentane in the presence of oxygen.(heat given off during reaction)

Naming branched complex substituents

begin by placing numbers on the substituent, going away from the parent chain. Place the numbers on the longest straight chain present. Consider the chain thats on that chain in the example, its a (2-methylbutyl group). Treat like its a miniparent with it own substituents.

Names produced by IUPAC rules

called systemic names

Assembling the systemic name of an alkane

carbon atoms of parent chain are numbered. numbers are used to identify the location of substituent called the LOCANT.

Hydrocarbons

compounds comprised of only C and H

For a combustion process, -ΔH

is called the heat of combustion. Can be conducted under experimental conditions using a device called the calorimeter. Careful measurement reveal that heats of combustion for two isomeric alkanes are different, even though the products of the reactions are identical. This difference can be used to compare the stability of isomeric alkanes. By comparing the amount of heat given off by each combustion process, we can compare the potential energy that each isomer had before combustion. This analysis leads to the conclusion that branched alkanes are lower in energy(more stable) than straight-chain alkanes. Very important way to determine relative stability of compounds.