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Intro to Alkanes


This is MCAT Organic Chemistry 1, we'll be covering Alkanes, and Substitutions. Alkanes or paraffins are carbon-hydrogen compounds that are links solely by single bonds. The formed the basic backbones in organic chemistry. You'll want to make sure that you memorize C1 through C12. C1 is methane, C2 is ethane, C3 is propane, C4 is butane, C5 is pentane, C6 is hexane, C7 is heptane, C8 is Octane, C9 is nonane, C10 is decane, C11 is undecane, and C12 is dodecane.

The first four have a regular names methane,ethane,propane,butane, but beyond that, they follow the same prefixes as regular polygons. Pentane, pentagon, hexane, hexagon, octane, octagon, and so on, and so forth. So if you remember C1 through C4, beyond that, all you'll need to know are the regular polygons, and you'll be okay. Now when we're naming alkanes there's a couple of general rules we want to follow.

First, we need to identify the longest chain, and name it. Second, we name, and number substituents (keep the numbers as low as possible on high priority substituents). And last we will add any isomer names. Generally you can distinguish between right and wrong answers that you can just do step one, and half of step two.

And that's just to name the substituents. Often by identifying the longest chain, and correct their identifying where the substituents are, you can cross out wrong answers. So, this is gonna be the two things you need to focus on. Normal substituents look like, and how to count how many carbons there are in the longest chain.

And we said that we want to make sure that you know the alkanes from C1 to C12. So as long as you count up to 12, you're gonna be fine on identifying the longest chain. Now the substituents that we want to know, and their priorities are 1.Carboxylic Acids, 2.Carboxylic Acids Derivatives, 3.Nitriles, 4.Aldehydes, 5.Ketones, 6.Alcohols, 7.Amines, 8.Alkenes, 9.Alkynes, and 10.Ethers.

So the carboxylic acid would be given preference over the aldehyde when you had to name a compound. And you would keep it's number as low as possible. Now there are a few common alkyl substituents that you're going to want to memorize. Let's identify these here.

This one right here has one, two, three carbons, so it's a propane. This happens to be the iso-propyl group. The second one here has one, two, three, four carbon, this is a butyl group. Since the attachment occurs on the second carbon. This is a sec-butyl. Or a second-butyl group.

Our third one here has one, two, three, four carbons. They are ranged in a T-shape. This is called the tert-butyl. Now here on the bottom left, we have one, two, three, four carbons. This is essentially iso-propyl group with an extra methylene here.

This is the iso-butyl. And our last one here, a tert-butyl with an extra methylene group. This extra group brings the total number of carbons to five, so this is a pentyl group. And in an arrangement like this, it's called a neo-pentyl. So, make sure you know these by name, how to draw them.

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