Types of Organic Compounds

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Types of organic compounds

Organic chemistry is an interesting mixture of understanding concepts and memorization. It’s time to memorize some things. We need to begin to be able to describe compounds so we can discuss them throughout this course. Many organic molecules contain reactive parts we call functional groups.

First, just like learning any new foreign language, you need to learn to count to ten. This is how we count in organic chemistry.

meth, eth, prop, but, pent, hex, hept, oct, non, dec

Let’s look at various types of compounds.

The Hydrocarbons

Hydrocarbons are compounds that are made up only of hydrogen and carbon atoms.

Alkanes

Alkanes are singly bonded carbon atoms, C-C. Alkane names typically have the –ane suffix. Knowing how to count in organic chemistry and the suffix, we can begin to name some compounds. We count the number of carbon atoms in the chain to get the prefix, and since they are all singly bonded, we use the alkane –ane suffix.

25. Write the names of the straight-chain alkanes that contain 5- to 10-carbon atoms.

5 ____________________

6 ____________________

7 ____________________

8 ____________________

9 ____________________

10 ___________________

Cycloalkanes

If an alkane is in a ring, it is a cycloalkane. We use the prefix cyclo- to name it.

26. Name these compounds.

Alkyl groups

When we are naming a piece of an alkane as a group on a more important part of a structure, we call that piece of alkane an alkyl group. We name alkyl groups with the –yl suffix.

If we want to write a generic alkyl group, because it is not important to the discussion we are having, we use the symbol –R. This stands for the “Rest” of the molecule.

Alkenes

Alkenes are hydrocarbons that contain a double bond between carbon atoms, C=C. Alkenes have the –ene suffix.

How about this compound that has four carbons and a double bond?

It should also be called some sort of butene, but we need a different name since the double bond is in the middle and not on the end. We have to tell which position the double bond is located, so we call it 2-butene.

And, once again, if the alkene is in a ring, we use the prefix cyclo-.

Cis/Trans

Alkene double bonds cannot rotate around because they are made using one p-bond locking them into place. This means that we will sometimes get some isomers because of the double bond.

If we draw out an alkene compound, we see that the C=C has four groups on it, two on the left side and two on the right side of the double bond.

If we draw out 2-butene, we have one hydrogen atom and one methyl group to put on each side of the double bond. We could put the methyl groups on top-top, bottom-bottom, top-bottom, bottom-top.

We see that we really only have two different structures here, not four. One of the structures has the CH3 groups on the same side of the double bond, while the other has the CH3 groups on the opposite side of the double bond. We use the prefix, cis-, to identify the same side and the prefix, trans-, to identify the opposite side.
Cis is Latin for “On this side of”. So, if I am reading cisatlantic literature, I’m reading literature from the same side of the Atlantic Ocean as myself. If I’m reading transatlantic literature, I’m reading literature from the other side of the Atlantic Ocean. (Cis = same, trans = opposite).

Not every double bond has cis-trans isomers, though. If both groups on the left side or both groups on the right side are the same, we cannot have cis or trans compounds.

27. Circle the compounds below that exhibit cis-trans isomerism.

Alkynes

Alkynes are hydrocarbons that contain a triple bond between carbon atoms, C≡C. Alkynes have the –yne suffix.

Aromatic Compounds

Although they look like cycloalkenes, aromatic rings have special properties. We’ll learn about these later, but for now, we want to realize that they are named differently. The simplest aromatic ring is benzene.

A phenyl group (abbreviated, Ph) is a benzene that is a group on another, more important chain.

Much like we use -R for a generic alkyl group, we use –Ar for a generic aromatic, or aryl, group. We use this when we want to indicate an aryl group is on a structure that we consider more important.

Hydrocarbons

Oxygen-containing compounds

Single bonds to oxygen

There are several types of functional groups that contain carbon-oxygen single bonds. Among these are alcohols, phenols, ethers, and epoxides. Alcohols are compounds with an –OH (hydroxyl) group on them. Phenols are a combination of phenyl groups and alcohols, hence the name. Ethers are compounds with an oxygen atom surrounded by two carbon atoms. An epoxide is an ether that is a 3-membered ring.

C-O single bonds

Carbonyl compounds

A carbonyl compound contains a C=O functional group. There are several of these carbonyl compounds.

Aldehydes, ketones, and esters are often fruity smelling compounds. They are a part of amino acids.
Carboxylic acids are acidic compounds.

Carbonyl compounds

28. Draw the Lewis structures for the following compounds. Make sure you use the normal bonding patterns for each atom.
a) CH3CHO
b) CH3CH2COOH
c) CH3CH2COCH3
d) CH3CO2CH3
e) CH3COCl
f) CH3CH2COOCH2CH3
g) CH3CONHCH3
h) CH3CO2H
i) CH3CON(CH3)2
j) CH3CH2OCH3
k) CH3CH2OH
l) CH3CHOHCH3

Nitrogen-containing compounds

Amines sometimes have a fishy smell. They are also usually basic compounds. Amines are also a part of amino acids. When the nitrogen of an amine has one carbon atom attached, it is a primary amine. When two carbon atoms are attached directly to the nitrogen atom, it is a secondary amine. When three carbon atoms are directly attached to the nitrogen atom, it is a tertiary amine. Nitro compounds tend to be explosive. You have probably heard of nitroglycerine or trinitrotoluene (TNT).

Nitrogen-containing compounds

Sulfur-containing compounds

Since sulfur is right below oxygen in the periodic table (the same group), sulfur forms some compounds similar to oxygen compounds. You’ll notice that thiol is an analog of alcohol and sulfide or thioether is an analog of ether. Thiols are found in many foul-smelling compounds. Thiols are responsible for the pungent smells of skunks.

Sulfur-containing compounds

2.29 Identify the circled functional groups in the following molecule.
Possibilities: Alcohol, amine, nitrile, amide, ether, ester, aldehyde, ketone, carboxylic acid, acid anhydride, thiol, disulfide, thioether, alkene, alkyne.