Organic Chemistry Reagents – How to Simplify into only 4 Categories
In the last section (Organic Chemistry Simplified Part 3), we found out how to find our nucleophile and electrophile. Now…time to look at the reagents.
There seems to be endless numbers of organic chemistry reagents. So – let’s see if we can find a way to classify these reagents and find a simpler way to look at them.
Categories of Organic Chemistry Reagents:
1. Oxygen
2. Hydrogen
3. Halogen
4. Metal
Well, that doesn’t seem too bad. I think you will agree… that is much simpler to look at and understand.
OK, let us take a look at each one…
1. Oxygen with and without hydrogen
Both types of oxygen reagents are considered oxidizing agents – they add oxygen. However, you tend to see them with specific functional groups.
Oxygen WITH hydrogen
Typically, you will see these the first two reagents with alkenes and ketones.
Alkene + H2O2 = Epoxidation
Ketone + RCO3H = Baeyer-Villiger oxidation
The last reagent (carboxylic acid) will be used as an acid in acid/base reactions (when it is a reagent). However, carboxylic acids are their own functional group as well.
Oxygen WITHOUT hydrogen
These reagents are typically much stronger oxidizing agents. Like before, they add oxygen to molecules. Here is what they will look like in your class:
Aldehyde + CrO3 = Carboxylic Acid
Ozone + O3 = Carbonyl Compounds (in this case – aldehydes)
Alkene + OsO4 = diol (two alcohol groups)
2. Hydrogen In-front and In-back of molecular formula
Here are the two most important things to know..
Hydrogen in-front = H+
Hydrogen in-back = H-
Therefore, “hydrogens in-front” act as a acids and “hydrogens in-back” act as nucleophiles.
Hydrogen IN-FRONT of structure
Alkene + HCl = Acid/Base Reaction (protonation)
Hydrogen IN-BACK of structure
Alkene + BH3 = Nucleophilic Addition
Carbonyl + LiAlH4 = Nucleophilic Addition
As you can see, the reactivity completely changes as you change where you put the hydrogen. This will help with Markovnikov vs. Anti-Markovnikov addition.
3. Halogens
Yes…you guessed it! These add halogens to organic molecules. Also as we will see, they can remove water to create an alkene.
Alkene + Br2 = Dibromide
Alcohol + SOCl2 = Halogenation (chlorination)
Alcohol + POCl3 = Dehydration (alkene formation)
In this last example, the key is to know that PHOSPHORUS LOVES OXYGEN! This will come up again when you study the wittig reaction…so keep this in mind.
4. Metals
These reagents are thought of as either nucleophiles or bases. Here is an easy way to separate the two:
Oxygen (with negative charge) prefers to be a base and all other atoms (with negative charges) prefer to to be nucleophiles.
Here are some examples of what you will typically see in your class:
Alkyl halide + NaCN = Nucleophilic substitution (SN2 reaction)
Carbonyl + CH3CH2MgBr (Grignard) = Nucleophilic addition
Alkyl halide + KOtBu (tert-butoxide) = Elimination (E2 reaction)
What to take home…
This does not cover everything you will see. However, this should give you a great starting place. From here, you should be able to start seeing trends you can use to help you on your exam or homework.
Coming up next!
In Organic Chemistry Simplified Part 5, you and I will go over how to dissect the reaction scheme to determine what is most important (what to focus on).