Nomenclature Part III

Hydrocarbons and Other Organic Molecules

Organic Chemistry

Organic Chemistry is the study of carbon chain-containing compounds.

Carbon has special bonding abilities that allow it to bond with itself to form long chains, rings, tubes, and even spheres!

Understanding Carbon Chemistry is essential for anyone considering the medical or pharmaceutical fields.

Hydrocarbons

Hydrocarbons are compounds composed of carbon and hydrogen.When the carbon-carbon chain contains only single bonds, the hydrocarbon is said to be Saturated.

Each carbon is “full” of hydrogens.A carbon is “full” when it has 4 single bonds.

When double or triple bonding occurs in the carbon-carbon chain, the hydrocarbon is Unsaturated.

The double and triple bonds can break and hydrogens can be added.

The Forms of HydrocarbonsWe will focus on three

1. Straight-Chain – all the carbons are in a straight line.

2. Branched-Chain – the carbon chain is not in a straight line, but has one or more branches.

3. Rings – the carbon chain forms a ring. The 6-carbon ring with alternating double and single bonds (benzene) is a very important chemical because of its strong structure. It has many applications.

There are also two other types…

Tubes

Spheres

Alkanes

An alkane is a saturated hydrocarbon.

Alkanes contain ONLY carbon and hydrogen.

Alkanes contain ONLY single bonds.

Alkanes can be either straight chains, or branched chains.

The generic formula for an alkane is CnH2n+2.

You should know the 1st 10…

1. CH4 Methane

2. C2H6 Ethane

3. C3H8 Propane

4. C4H10 Butane

5. C5H12 Pentane

6. C6H14 Hexane

7. C7H16 Heptane

8. C8H18 Octane

9. C9H20 Nonane

10. C10H22 Decane

Structural IsomerismStructural Isomerism is when two molecules have the same chemical formula, but different structural geometry.

Alkanes made of branched carbon chains are structural isomers of the straight chained hydrocarbons.

The “branches” on branched chains are called Substituents.REMEMBER! The chain is always named for the largest number of consecutive carbons. The longest number of consecutive carbons may not be the straight chain as it is drawn on the paper. Always count the carbons from every angle to find the root name.

Structural Isomers of ButaneC4H10

Butane

n-butane

2-methylpropane

isobutane

Knowing how to name Organic Molecules is IMPORTANT because…

1. There are two molecules with the formula C4H10.2. Due to their very different shapes, they have very

different chemical properties.3. We cannot identify them by formula alone.4. Drawing them to identify them is inconvenient,

especially when typing.5. There are far too many organic molecules to

name each one individually and be familiar enough with all of them to communicate.

So we came up with a set of rules where the name tells you the shape of the molecule and where stuff goes on it. i <3 O-Chem!!!

Substituents

Substituents are “things” attached to a carbon chain that are not hydrogen.

Substituents can be…1. Carbon chains that are smaller than the

main chain

2. Halogens

3. Organic Subgroups

We will learn how to name all 3!!

The Root name of a Hydrocarbon

The root name of a hydrocarbon is always determined by the longest continuous carbon chain.

If the longest chain contains 6 carbons for example, the root name is hexane.

If the longest chain only contains 3 carbons, the root name is butane.

The root name of a hydrocarbon is always the LAST part of the name.

Naming the SubstituentsSubstituents on the main carbon chain are named using numbers and prefixes.

The number comes first, indicating which carbon in the chain the substituent is on.

The carbon chain should be numbered in such a way that the substituents are on the lowest numbered carbons.

The number is followed by a hyphen.The substituent is then represented by its prefix. (common prefixes on next 2 slides)

If there are more than one substituent on a chain, they are listed in alphabetical order, each one followed by a hyphen.

For example, 3-ethyl-2-methylhexaneThe order does not reflect the physical order on the chain.

Some Common Substituent PrefixesSmaller Alkane Substituents on a larger chain are named by using the root and replacing –ane with -yl.

Methane Methyl-Ethane Ethyl-Propane Propyl-Hexane Hexyl-

Halogen Substituents are named by replacing –ine with –o.

Chlorine cloro-Fluorine Fluoro-Bromine Bromo-Iodine Iodo-

Other Common Substituents-OH Hydroxyl--NH2 Amino-

Important Akyl Substituents

Carbon Chains with Multiple Copies of the Same Substituent.

If there are 2 or more of the same substituent on the chain they can be combined using the Latin prefixes (mono, di, tri, tetra, etc…)

For example, 2,4-dimethyldecane, indicates that there is an methyl group on both carbon #2 and carbon #4

The carbon numbers are listed in numerical order and separated by comas.A hyphen follows the last number.The prefix is added to the beginning of the substituent’s prefix.

Name the Isomers of Butane, Pentane, & Hexane using the formal rules…

Hydrocarbons that form LOOPS!

Cyclic Hydrocarbons occur when the hydrocarbon chain forms a ring.

There must be at least 3 carbons to make a ring, because 2 carbons can only be linear. ;)

Cyclic Hydrocarbons have the generic formula CnH2n.Naming Cyclic Hydrocarbons

They follow the rules for naming alkanes, but the prefix cyclo- is added to the root name.Example: a 6-carbon ring is called cyclohexane.

The First 4 Cyclic Hydrocarbons

Cyclic Hydrocarbon GeometryThe first two cyclic hydrocarbons (cyclopropane & cyclobutane) have a strained geometry because the bond angles are so much smaller than that of a tetrahedral carbon.

For this reason they are very reactive compared to linear alkanes.

Cyclopentane and Cyclohexane have a stable geometry because the bond angles are very close to that of tetrahedral carbon.

This stability lowers the reactivity of these two.

Cyclic hydrocarbons greater than hexane loose this stability because the bond angles once again become strained, as they deviate from that of tetrahedral carbon.

Like the smaller rings, these too are very reactive.

Unsaturated HydrocarbonsUnsaturated Hydrocarbons contain either a carbon-carbon double bond, or a carbon-carbon triple bond.

These molecules have special properties because they involve pi bonds, which do not allow the freedom of rotation that saturated hydrocarbon chains, which contain only sigma bonds, have.

There are two types, Alkenes & Alkynes.

AlkenesAlkenes are unsaturated hydrocarbon chains that contain one or more double bonds.

Alkenes have the generic formula CnH2n

Naming AlkenesAlkenes are named using the same roots as the alkanes, but the –ane is changed to –ene.The lowest numbered carbon involved in the double bond is represented by that number followed by a hyphen attached to the beginning of the root.

Example: H3C-CH=CH-CH2-CH3 is called 2-pentene

If there is more than one, the Latin prefixes are used, but this time it goes in front of the –ene.

Example: H3C-CH=CH-CH=CH-CH3 is called 2,4-hexadiene

AlkynesAlkynes are unsaturated hydrocarbon chains that contain one or more triple bonds.

Alkynes have the generic formula CnH2n-2

Naming AlkynesAlkenes are named using the same rules as the alkenes, but the –ene is changed to –yne.

The triple bond in Alkynes means that this part of a hydrocarbon chain is always linear in its geometry.

The geometry of Alkenes is not as simple, and must be discussed further…

Cis-Trans IsomerismThe restricted rotation around a double bond leads alkenes to have a property called Cis-Trans Isomerism.When substituents are located one on each carbon of the double bond, they can exist either both on the same side of the bond, or on opposite sides.

A Cis- Isomer occurs when both substituents are on the same side of the bond.

A Trans- Isomer occurs when each substituent is on a different side of the bond.

Remember there must be substituents on each carbon in the bond for this to occur.

Naming Cis-Trans Isomers

Cis-Trans Isomers are named as other alkenes with one addition…The cis- or trans- prefix is added before the number indicating the first carbon in the double bond.

Aromatic Hydrocarbons

Aromatic Molecules are a special group of unsaturated hydrocarbons.

So named due to the notable smell that all aromatic molecules seem to have…

Benzene is the simplest example.

C6H6

Benzene’s Structure is more accurately represented like this

Research has revealed that the bonds in a benzene ring are actually all equivalentThe double-single bonds exist in resonance, and are more like a hybrid, or a combination of a double and single bond.The structure is incredibly stable, and is very important in organic reactions.Benzene is also a very important solvent for non-polar chemicals (benzene is to organics as water is to salts).

Benzene and Substituents

Benzene can hold substituents by substituting “things” for hydrogens just like other hydrocarbons.When there is only one substituent, benzene is named with the substituent prefix.

Examples are chlorobenzene and methylbenzene.

When there are two substituents, however there are more rules. :D

2 Substituents on BenzeneIf the same, the Latin prefixes are used

If different they are listed alphabetically

They can be arranged in 3 ways…1. On adjacent carbons

“Ortho” – represent by o-

o-dibromobenzene

2. With one carbon in between“Meta” – represented by m-

m-bromomethylbenzene

3. On opposite carbons“Para” – represented by p-

p-bromochlorobenzene

Benzene as a Substituent

Benzene does not make the best substituent because it is so BIG.

Big molecules take up a lot of space, and don’t fit easily on carbon chains, but it happens.

Benzene has the prefix phenyl- when it is used as a substituent.

Some Common Aromatic Hydrocarbons

The Organic SubgroupSome Organic Molecules contain atoms other than carbon and hydrogen.

We have already seen examples of this with the halogen substituents.Most of the time, these “other” atoms appear in repeating patterns that are easy to recognize, called organic subgroups.

Organic Subgroups are also called Functional Groups.

This is because each organic subgroup has its own characteristic chemical behaviors.

Some Chemical ShorthandThe following are symbols used to represent (generically) groups of chemicals that behave similarly.Review…used to describe the ions in salts.

M+ = metal cationX- = nonmetal anion

New…These you must know to understand Organic Subgroups.

X = halogenR = hydrocarbonR’ = hydrocarbon different from RR’’ = hydrocarbon different from R & R’

The Common Functional GroupsClass Functional Group Generic Formula

Halohydrocarbon -X R-XAlcohol -OH R-OH

Ether -O- R-O-R’Aldehyde -CŐH R-CŐH

Ketone -CŐ- R-CŐ-R’Carboxylic Acid -CŐOH R-CŐOH

Ester -CŐO- R-CŐO-R’Amine -NH2 R-NH2

Amide -CŐNH- R-CŐNH-R’

Functional Groups 2D with Lewis Dot (better representation of the shape)

AlcoholsAlcohols are classified by the presence of a hydroxyl group (-OH).

Alcohols are named by giving the carbon number the hydroxyl group is on, followed by a hyphen. Next comes the root name, replacing the ending -e with –ol.

Examples:CH3OH is methanol

CH3CH2CH2OH is 1-propanol

CH3CHOHCH3 is 2-propanol

Classifying AlcoholsAlcohols are classified based on the number of hydrocarbons bonded to the carbon where the hydroxyl group is located.

# of ‘R’ Groups

Generic Formula

Classification

1 R-CH2-OH Primary

2 R-(R’)CH-OH Secondary

3 R-(R’)(R”)-C-OH Tertiary