Naming alkanes
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Representing Structures of Organic Molecules
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Naming Simple Alkanes
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Naming Alkanes with Alkyl Groups
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Correction - 2-Propylheptane should never be the name!
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Common and Systematic Naming-Iso, Sec and Tert Prefixes
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Organic Chemistry Naming Examples 1
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Organic Chemistry Naming Examples 2
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Organic Chemistry Naming Examples 3
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Organic Chemistry Naming Examples 4
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Organic Chemistry Naming Examples 5
Common and Systematic Naming-Iso, Sec and Tert Prefixes Common and Systematic Naming-Iso, Sec and Tert Prefixes
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- Let's see if we can get the molecular structure for
- butylcyclopentane.
- So you just break this up the way we've done it in the last
- several videos, the suffix is -ane, so it is an alkane, all
- single bonds.
- So single bonds.
- It's pentane, so we're dealing with five carbons on the base,
- or on the backbone.
- So this is five carbons and it's a cyclopentane, so it's
- five carbons in a ring.
- So its five-carbon ring is the backbone, and then we have a
- butyl group added to that five-carbon ring.
- Now, you might say, hey, Sal, how do I know which
- carbon to add it to?
- When you're dealing with a ring and you only have one
- group on the ring, it doesn't matter.
- Let me just show you what I mean.
- So let's draw the five-carbon ring.
- Let's draw the cyclopentane.
- So it'll just be a pentagon, so one, two, three, four,
- five, and it's a ring, so you can connect them.
- One, two, three, four, five.
- Now, it doesn't matter where I draw the butyl group.
- It's all symmetric around there.
- We just have a ring and it's connected to a butyl group at
- some point.
- It'll start to matter once we add more than one group.
- So we can just pick any of these carbons to add
- the butyl group to.
- Now, just as a review, the but- prefix, that refers to,
- remember, methyl, ethyl, propyl, or meth-,
- eth-, prop-, but-.
- This is four carbons.
- This is a four-carbon alkyl group.
- So let me just add it here.
- I could have added it to any of these carbons around this
- cyclopentane ring.
- So if I just add it right here, so I'm going to have
- four carbons.
- So one, two, three, four.
- That is the butyl part of this whole thing.
- And then let me just attach them up.
- So you might be tempted to just draw this right there.
- And actually, this would be right.
- This is butylcyclopentane.
- But a question might arise.
- I just happened to connect the cyclopentane to the butyl at
- this first carbon on the butyl right there.
- I could have just as easily done it like this.
- I could have just as easily had it like this, where-- let
- me draw my butyl again, so I have one, two, three, four.
- So, once again, this is a butyl, but instead of being
- bonded to the cyclopentane on my first carbon, maybe it's
- bonded right here.
- Let me do it with that yellow color.
- Maybe it's bonded right here.
- This seems like maybe this could also be
- butylcyclopentane.
- It looks like we have a butyl group.
- This is a butyl right here.
- I drew a butyl group right over here, and I also drew a
- butyl group right over here.
- But these are fundamentally two different molecular
- structures.
- I'm touching the first carbon here.
- I'm touching the second carbon over here.
- Now, there's two ways to differentiate this.
- One is the common naming and one is the systematic naming.
- So let me differentiate between the two.
- So in the common naming, and this can get a little bit
- involved, and this frankly is probably the most complicated
- part of naming organic compounds.
- Systematic is often more complicated, but it's easier
- to systematically come up with it.
- So there's a common and then there's a systematic.
- So the common way of doing it is, if you just say
- butylcyclopentane, that implies that you are bonding
- to the first or, depending on how you view it, the last
- carbon in the chain.
- So this right here is butylcyclopentane.
- This right here is not just butylcyclopentane.
- What you would do is you definitely have a cyclopentane
- ring, so this would definitely be a cyclopentane.
- Let me put some space here.
- This is definitely going to be a cyclopentane.
- And you do have a butyl group on it, so we do have a butyl
- group, but because we are bonded-- we aren't bonded to
- the first carbon.
- We're bonded to a carbon that is bonded
- to two other carbons.
- We call this
- sec-butylcyclopentane, so this is sec-.
- And everything I'm doing is obviously free-hand.
- If you were to see this in a book, the sec- would be
- italicized, or sometimes it would be written as
- s-butylcyclopentane.
- And this sec- means that we have attached to a carbon that
- is touching two other carbons.
- So you look at the butyl group, and say, well, which of
- these carbons is attached to two others?
- It's either that one or that one.
- And regardless of whether you're attached to this or
- this, if you think about it, it's fundamentally the same
- molecular structure.
- So that's what you do when you're attached to that guy
- right over there.
- But what about the situation where we're dealing with just
- the common names right here?
- What about the situation where it looks like this?
- So we have our cyclopentane right there, and we have a-- I
- guess we could call it a butyl group.
- It'll have four carbons in it, but let's say that the four
- carbons look something like this.
- Let's say there are four carbons, so we have one, two,
- three, four carbons and we're bonded to this
- one right over here.
- So whenever you're bonded to one end of the four-carbon
- group and it branches off at the other end, and it seems a
- little complicated, this only deals for alkyl groups below
- five or six carbons, this we call an isobutyl group.
- So let me write this down.
- So this right here, is sec-butyl, or s-butyl
- sometimes for short.
- This right here, this right there is iso-butyl.
- It's actually-- iso- that is an iso-butyl group.
- And then the last thing to worry about when you're
- dealing with butyl groups is something like this.
- Let me draw it.
- So you could also draw four carbons like this.
- You have one carbon, two, three, four.
- One, two, three, four carbons and you're attached over here.
- Now this naming, this group right here-- and you're going
- see the systematic naming is much
- easier for these compounds.
- This group right here, over here the carbon you're
- attached to is attached to two other
- carbons, so it is sec-butyl.
- When you're attached to three carbons, it is t-butyl, or
- tert-butyl, so this right here is a tert-butyl group, or
- sometimes called a t-butyl.
- And I really want you to understand
- the difference here.
- The common naming, it's easier to say and easier to spell,
- but it's sometimes a little confusing.
- This is just straight up butyl so you would call this
- butylcyclopentane.
- This is sec-butyl, because you have this guy
- connected to two carbons.
- That's where the sec- comes from.
- Sometimes it'll be s-butyl.
- So this could be called sec-butylcyclopentane or
- s-butylcyclopentane.
- This, because we're attached to the end away from this
- branching off, is still a butyl group, since we have
- four carbons.
- But since we're attached here, this is iso-butyl, so this is
- iso-butylcyclopentane,
- And then finally, since the carbon we're attaching to is
- attached to one, two, three other carbons, it is a
- tert-butyl or a t-butyl group.
- So this is t-butylcyclopentane.
- That's the common naming.
- So maybe I should clear out systematic here just so it's
- clear to you that everything we've done
- here is common naming.
- So let me write it down.
- It won't hurt to write them down again because the more
- familiar you are with these, the better.
- So this is just butylcyclopentane.
- This is s- or sec- butylcyclopentane.
- And this is iso-butylcyclopentane.
- I'm going off the screen here.
- And then finally, this is tert-butyl, or
- t-butylcyclopentane.
- Now, I said these are the common naming.
- What are the systematic naming?
- Well, in the systematic, this is still butylcyclopentane.
- So let me write this down.
- Systematic, this is still
- butylcyclopentane, which makes sense.
- This is very clearly a cyclopentane.
- This is very clearly a butyl group.
- But in the systematic naming, what we try to do is we try to
- name this group right here just as we would name a
- traditional chain, but we ended it with an -yl.
- So if you look at this right here, what we do is we just
- consider the chain where we attach.
- We attached over here, so the longest chain from that point
- is there and there.
- So if you look at it like that, it looks like you have
- one, two, three carbons, and you have one carbon attached
- on the beginning.
- So this little group right here in the systematic naming,
- this looks like a one, two, three.
- Three carbons, that's the prop- prefix, so we're dealing
- with a prop-, and it's all going to be one group, so it's
- a propyl group.
- This is a propyl group, but it has a methyl-- remember, meth-
- is one carbon.
- It has a methyl group attached on the first carbon.
- So this is 1-methylpropyl.
- Now, that describes just the group.
- 1-methylpropyl describes just this part right here.
- That describes just that right over there.
- And then to have the whole compound, to describe the
- whole compound, you put this in parentheses, so this is the
- systematic naming.
- So 1-methyl-- I put an L there.
- Let me do it in the same color.
- 1-methyl, because you're starting
- where you're attaching.
- So 1-methyl, you have a methyl group right there on that
- first carbon.
- It's a propyl chain.
- One, two, three, propyl, and then you would say
- cyclopentane.
- That's the systematic name for that.
- Now if you look at this one right here, and the common
- name is iso-butyl, what you do is you
- look at where we attach.
- Where we attached is one, two, three carbons.
- So once again, I'm doing that same one, two, three carbons.
- So once again, this is a propyl.
- Prop- is for three, but with a methyl group now is attached
- to the one, two, the second carbon.
- So this is 2-methyl.
- Let me make some space here.
- This is 2-methyl.
- So that describes this group right here.
- That describes this entire group cyclopentane.
- Remember, this is a systematic name.
- You might sometimes see this referred to as
- iso-butylcyclopentane or 2-methylpropylcyclopentane.
- And this is actually a -yl.
- I spelled it wrong.
- And then finally, we do the same exact idea here, but it
- becomes a little bit more interesting.
- Over here, we are attached to this carbon and the longest
- chain I can do starting with that carbon is just one chain
- right there.
- So we just have a two-carbon chain, right?
- One, two.
- The prefix for a two carbon is ethyl, or eth-.
- Eth-, and since it's a group, ethyl.
- And then we have two methyl groups attached right over
- there, and it's attached on the one carbon, right?
- This is one and this is two.
- We call the one carbon where we are attached
- to the broader chain.
- So what this is going to be, you would actually write one
- comma one to show that we have two groups attached to the
- first carbon and both of them are methyl.
- So we write 1,1-dimethyl, di- for two, dimethyl.
- So this entire group right here, which we also called
- t-butyl, in systematic naming is 1,1-.
- We have two groups attached to this first carbon.
- 1,1-dimethylethyl.
- That's this whole thing.
- This is the ethyl, and then we have two methyls attached
- there. that's why we write 1,1-.
- They're both attached to the one.
- We have two of them.
- That's why we wrote di- over there.
- So it's 1,1-dimethylethyl- and then finally, cyclopentane.
- So hopefully, that doesn't confuse you too much.
- I think if you watch the video over and over and try to
- practice it with your own problems, you'll see that the
- systematic name way is actually
- pretty, pretty logical.
- And actually, if you have more than five or six carbons in
- the group, they always or they tend to always use the
- systematic naming.
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