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Hydrocarbons and Haloalkanes

Introduction

Organic compounds are divided into different classes of compounds based on the elements that are present in the functional groups that may be present.

The next slide is a chart I found at Biology Corner to give you an idea of the number of compounds out there.

Introduction

Hydrocarbons

The simplest of the organic compounds are a large group of compounds called the hydrocarbons.

A hydrocarbon is an organic compound containing only the elements carbon and hydrogen.

Hydrocarbons

There are further subdivisions according to how the carbons and hydrogens combine.

Compounds characterized by open chains of carbon to carbon bonds are considered to be acyclic or aliphatic.

Those compounds whose chains of carbons form a ring considered to be cyclic or aromatic.

Hydrocarbons

The aliphatic hydrocarbons are further subdivided into classes based on the type of bonding that is present between the carbons.

Alkanes

The alkanes are acyclic hydrocarbons in which all of the carbon to carbon bonds are single covalent bonds (single bonds).

The alkanes are also considered to be saturated hydrocarbons because they will hold no more hydrogens.

Alkanes

The word ‘alkane’ comes from a prefix and a suffix. The prefix “ALK-“ refers to the Aliphatic hydrocarbon and the suffix ”-ANE” refers to the presence of all single bonds.

Alkanes

The characteristic type of reaction for the alkanes is substitution or replacement since it would be necessary to replace a hydrogen to combine the molecule with another substance.

Alkanes

Alkanes have several alternate names:

Paraffin series.

Methane series.

This series gets its name from the very first member of the class, the gas methane.

Alkanes

All of the members of the alkanes have a molecular formula that may be determined by the general molecular formula of the class: CnH2n+2.

The integer “n” is the number of carbons.

Alkanes

In determining the general molecular formula, you simply substitute the number of carbons where the “n” is.

Naming the Alkanes

When naming the alkanes we use the same rules for nomenclature established by the International Union of Pure and Applied Chemists (IUPAC).

Naming the Alkanes

Here are the rules:

First, name the longest chain of carbons.

Then, name the carbon side chain(s) from largest to smallest.

Give addresses for all side chains using smallest numbers.

Naming the Alkanes

The name is always written from right to left but it is read from left to right.

The carbon chains are always identified by the appropriate prefix for the number of carbons in the chain.

The longest chain would have the suffix”-ANE”.

Carbon sidechains are also called radicals and they are identified by the appropriate prefix followed by the suffix “-YL” which identifies a radical work carbon sidechain.

IUPAC Prefixes & Suffixes

Naming Alkanes

Name the alkane of one carbon.

Naming Alkanes

Name the alkane of two carbons.

Naming Alkanes

Name the following alkane.

Naming Alkanes

So working through this step-by-step:

We count the number of carbons in the chain which is six. Looking at the prefixes this gives us “HEX”. In looking at the bonds we see that they are all single bonds which gives us the prefix “ANE”. We now know we are dealing with hexane.

Naming Alkanes

So working through this step-by-step:

We see a side chain coming off the second carbon. This sidechain consists of one carbon and three hydrogen. Looking at the prefixes we see the prefix ”METH” which means one and the suffix “-YL” which indicates it's a side chain. We now know this word is methyl.

Naming Alkanes

So working through this step-by-step:

Now that we have named the main chain and the side chain, we have to indicate where the side chain actually appears. The rule of using smallest numbers comes into play . If you start from the right most side it is five; if you start counting from the left hand side it is two. Since we always use the smallest number, we go with the number ”2”.

Naming Alkanes

So working through this step-by-step:

This gives us the name “2-methyl hexane”

Alkenes

The alkenes are aliphatic hydrocarbons in which one of the carbon to carbon bonds is a double bond (double covalent bond).

The alkenes are considered to be unsaturated hydrocarbons because the double bond could be broken allowing for the addition of more hydrogen.

The prefix “ALK-“ once again refers to the aliphatic hydrocarbon but the suffix “-ENE” refers to the presence of at least one double bond between carbons.

Alkenes

The characteristic type of reaction for the alkenes is by addition since it would be possible to add across the double bond when combining with another substance.

Alkenes

There are several other names for this series:

Olefin series.

Ethene series.

The ethene series gets its name from the very first member of its class, ethane.

Alkenes

The general molecular formula of this class is CnH2n.

As with the alkanes, you simply insert the number of carbons for the integer ”n” to produce the molecular formula.

Naming the Alkenes

As with the alkanes, there are rules for naming the alkenes:

First, find the longest continuous chain of carbons containing the double bond.

Give the address of the double bond by using smallest numbers. You can omit this step if the address cannot be confused.

Number the carbons in the longest chain so that the carbons on either side of the double bond have the smallest addresses.

The address of the carbon next to the bond which has the smallest numbered address is the address of the double bond.

If the double bond is between carbons three and four then the address would be three.

Naming the Alkenes

Name the carbon sidechain(s) from largest to smallest. Give addresses for all side chains using the addresses for the carbons as determined by the address of the double bond.

The name is always written from right to left but is read from left to right.

Carbon chains are always identified by the appropriate prefix for the number of carbons in the chain. The longest chain would have a number preceding the prefix identifying the address of the double bond and would have the suffix “-ENE” because of the double bond.

Carbon sidechains are also called radicals and they are identified by the appropriate prefix followed by the suffix “-YL” just like in the alkanes.

Naming the Alkenes

I will not cover naming two or three carbon alkanes as I feel these are fairly self explanatory.

Naming the Alkenes

With the four carbon alkene, we see there is the potential that the double bond could be located between carbons one and two or carbons two and three.

Don't over think this: always use the lowest number. If it is between one and two then it is 1-Butene and obviously if it is between two and three it is 2-Butene.

Naming the Alkenes

Now let's try naming the big alkene:

Naming the Alkenes

Follow the rules, first count the total number of carbons in the longest chain. The chain has six carbons and the prefix for six is hex. We know that we are dealing with hexene.

Naming the Alkenes

Next we determine the double bond, and it is either between carbons four and five or two and three. We always use the lowest numbers so it would be between two and three. Using the smallest number we get the number two. At this point we know we have 2-hexene.

Naming the Alkenes

Now we have to determine the side chain. This is the same as the last example so we know that we are dealing with one carbon which gives us methyl.

Naming the Alkenes

Now comes the fun part, we have to count from the same side where we have the double bond. In this case it is on the fifth carbon from the right. This gives us the number 5.

Do not fall into the trap of starting from the closest end. Always start from whichever end the covalent bond starts.

Naming the Alkenes

The formal name is 5-methyl 2-hexene.

Alkynes

The alkynes are aliphatic hydrocarbons in which one of the carbon to carbon bonds is a triple bond (triple covalent bond). The alkynes are considered to be unsaturated hydrocarbons because the triple bond could be broken allowing for the addition of more hydrogens.

Alkynes

By now you should know what the prefix “ALK” stands for. The suffix “-YNE” refers to the presence of at least one triple bond between the carbons.

Alkynes

The characteristic type of reaction for the alkynes is addition since it would be possible to add across the triple bond when combining with another substance.

Just like the other classes, this one has several alternate names:

Acetylene Series.

Ethyne Series.

Alkynes

All the members of the alkynes have a molecular formula that may be determined by the general molecular formula of the class: CnH2n-2.

Naming Alkynes

Naming this class follows very similar rules to that of the alkenes. I will not cover them in detail during the lecture. As with any of the classes we have discussed so far, pay particular attention to the suffixes. –ENE, -ANE, -YNE all mean different things and this is where you will get into trouble if you are not careful.

Aromatic Hydrocarbons

The aromatic hydrocarbons are those organic compounds which are comprised of only the elements carbon and hydrogen arranged so that at least some of the carbons are linked together to form a ring.

Sometimes they are called cyclic or closed chain.

The carbocyclic hydrocarbons are those with only carbon in their rings.

Cycloalkanes

The cycloalkanes are also known as cyclanes.

They are carbocyclic hydrocarbons similar to the alkanes, except for the fact they form rings instead of open chains.

Cycloalkanes

All of the members of the cyclanes have a molecular formula that may be determined by the general molecular formula of the class: CnH2n

Cycloalkanes

The smallest of the cycloalkanes is cyclopropane. It is a three carbon ring with two hydrogens attached at each carbon and single bonds between all carbons.

Cycloalkanes

The prefix “cyclo-“ refers to the ring structure, the prefix “prop-“ Refers to the three carbons in the chain, and the suffix “-ane” refers to the single bonds joining them.

Cycloalkanes

Cyclobutane would be the next member. It is a ring of four carbons with two hydrogens at each carbon and single bonds between all carbons

Cycloalkenes

The cycloalkenes are carbocyclic hydrocarbons similar to the alkenes in that they have at least one double bond between two of the carbons and are different because they form a ring instead of a chain.

The most prominent member of this group is the compound benzene.

Cycloalkenes

Benzene is a ring of six carbons with what appears to be alternating double bonds between the carbons in a single hydrogen attached to each carbon.

Cycloalkenes

Benzene has the molecular formula C6H6.

Benzene's structural formula appears to be simply a ring of carbons with the alternating double bonds. The problem is that in reality it does not actually happen this way.

Cycloalkenes

What actually happens is that the alternating double bonds are resonating between all of the carbons. This bouncing back and forth of the double bonds is created by an interesting physical property of the valence electrons called resonance.

Cycloalkenes

Due to the resonance that occurs in benzene and its family of compounds the type of reactions they undergo is not what one expects from an unsaturated compound.

Cycloalkenes

Benzene and the majority of the aromatic compounds react not by addition as noted with the aliphatic unsaturated compounds but instead by the replacement or substitution of the hydrogen(s).

Alkyl Halides

The Alkyl halides or haloalkanes appear as an alkane that has had one or more of its hydrogens replaced by a member of the halogen family found in group 7 of the periodic table.

Alkyl Halides

As a group this class of organic compounds has the general formula R-X.

The term “R” refers to the alkyl group and the “X” stands for the halogen.

Alkyl Halides

The rules for naming this class of compounds is similar to naming the alkanes in that the halogen is treated as the smallest sidechain and should be addressed if its position could be confused.

Alkyl Halides

The simplest of the alkyl halides would include the compound chloromethane (methyl chloride).

Alkyl Halides

The continued replacement of the hydrogens in methyl chloride by chlorination would eventually yield methyl trichloride (trichloro methane).

Alkyl Halides

When the final hydrogen is replaced with chloride the result would be methyl tetrachloride (tetrachloromethane). This is commonly referred to as carbon tetrachloride or carbon tet.

Alkyl Halides

Carbon tetrachloride is a very good organic solvent and is nonflammable so it was also using fire extinguishers at one time.

Unfortunately, its vapors are very toxic and can cause death.

References:

The following Textbook References were used to create this presentation:

Funeral Service Chemistry by Professional Trade Schools

Embalming: Theory, History, and Practice by Robert G. Mayer (5th Edition).

Charts were taken from the textbook unless otherwise indicated

Pictures and art used in this presentation have the reference and location stored in the graphic. Please hover the mouse over the image to find where it was obtained.

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