Constitutional isomers of C5H12O | Alcohol & Ether – Dr K
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Constitutional isomers of C5H12O | Alcohol & Ether – Dr K

October 12, 2019


The question is asking to draw all
constitutional isomers for C5H12O. Since this chemical formula fits in the
general formula of CnH2n+2O, that means C5H12O can be an
alcohol with a OH group or an ether which has an oxygen sandwiched between
two carbons. We’re going to use a systematic way to draw out all the
isomers that way we won’t be drawing randomly and miss out any structures.
Let’s start by drawing a five carbon chain alcohol meaning five carbons
connected straight in a row and then we place a OH at the first carbon that
will give us our first structure. We can then move the OH group to the second
carbon like this and then we move again to the third carbon and that will give
us our third structure. Now if we move OH to the fourth and the fifth carbon
will essentially get back the first two structures that we have already drawn, so,
that’s all for the five carbon chain. Moving on to four carbon chain alcohol
we draw four carbons straight in a row and then we place that extra carbon left,
fifth carbon on carbon number two. Let’s start by placing OH on the first
carbon like this and then working with the same four carbon chain we’re gonna
move the OH to the second carbon like that and then if we move it to the third
carbon it will also give us another isomer so we’re gonna keep that and
lastly if we move the OH to the fourth carbon like that. It will give us yet
another isomer so we’re gonna keep all of this and it looks like we have
exhausted all the possibilities for the four carbon chain, so that’s all that we
have. Now can we move on to three carbon chain. Yeah, looks like it’s possible so
if we place three carbon straight in a row the only way we can place the extra
two carbons would be on carbon number two. If we place them on the first carbon
or the third carbon we’ll just end up drawing the structures that we have
already drawn, so there’s only one way to add the OH group, placing it on one
of the carbons. So we’ve exhausted the three carbon chain. Do you see how we
drew the alcohols in a systematic way? We started with five carbon chain so we
drew five carbon straight in a row and now we start moving the OH
carbon number one all the way to carbon number three and then we exhausted all
the possibilities. Then we move on to four carbon chain so we have four carbon
chain with the fifth carbon sticking on carbon number two so we keep that
structure and then we stick OH on carbon number one and then we keep
moving it until we exhausted all possibilities and then we move on to
three carbon chain. Since it’s impossible to have two carbon chain with five
carbons so we stop that at three carbon chain. Here are the eight alcohols we
have drawn. Let’s move on to draw ethers. Start with one carbon before oxygen then
we place the remaining four carbons like this so we have C O and then four carbons. Now keeping this one carbon before oxygen let’s try out to see if we can
shorten the four carbons at the end. We’ll draw in a different way like this
CO and then three carbons and then we stick the extra carbon on carbon number
one. So that’s an isomer. Now if we move that extra carbon to the second
carbon we will actually get a different isomer. Now looks like we are done with
this set. So let’s explore placing two carbons before oxygen and so that means
we have three carbons after that, so we have two carbons before oxygen and three
carbons after the oxygen, that’s one way of drawing it. Repeating the same thing
that we did with the previous set let’s shorten the carbon chain of the oxygen
let’s make it two carbon and place that extra carbon like this. Since there’s no other way we can
shorten the chain at the back we are pretty much done with this set. Do we
need to draw three carbons before oxygen followed by two carbons like meaning CCOCC? Nope. Because that would give us the same
structure that we have already drawn, so that’s all the ethers we can draw for
C5H12O. Here’s how they look like completed with hydrogens. We have a
total of 5 ethers for C5H12O combine with the 8 alcohols that we have drawn,
C5H12O has a total of 13 isomers. I hope you find the video helpful. Do
subscribe. Thanks for watching and I’ll see you in the next video.

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