Naming simple alkanes | Organic chemistry | Khan Academy

Naming simple alkanes | Organic chemistry | Khan Academy


So when we name organic
molecules, the core of what we think about is just how many
carbons form the chain or form the ring that we’re
looking at? So let’s say I have something
like this. And hopefully, you’re reasonably
familiar with what this represents. And I’ll review it
a little bit. So let’s say I have something
like this. Let’s say that that
is the molecular structure right there. And so the first question you
should be asking is how many carbons are there? And some of you might
say, wait, how is that even a molecule? And just as a review, the
end point of every line represents a carbon. So that’s a carbon, that’s a
carbon, that’s a carbon, that’s a carbon, that’s a
carbon, that’s a carbon. And we have one, two, three,
four, five, six carbons and we have no double bonds. So if you have all of that
information you’re ready to name this molecule. And before I actually name it,
let me just kind of give you all of the different prefixes. So if you have one carbon,
the prefix is meth-. If you have two carbons,
the prefix is eth-. And it’s good to memorize
at least up to about 10. And actually it kind of
repeats after that. If you have three carbons,
the prefix is prop-. Prop- like propane, and you’ve
heard of ethane and methane. So you’ll see all
of that soon. Four, you’re talking
about but-. Five, and after five it kind
of becomes the traditional prefixes that we associate with
a lot of these numbers. So at five, it’s pent-,
like pentagon. Six, it’s hex- like hexagon. Seven is hept-. Eight is oct-, like octagon. Nine is non-. Ten is dec-. And then after that it kind of
starts to have a pattern here, and you’re not going to really
deal with things much beyond the teens, but I’ll just write
them down here just out of interest. Eleven is undec-. And for those of you who know
French, I’m not one of them, but I know that one in French
is une, or in Spanish, uno. So it’s 1 and 10, 11. Twelve is dodec-. Do or dos, if you’re speaking
Spanish, for 2. Dec for 10, 2 and
10, that’s 12. Thirteen, you could imagine
what it’s going to be. It is tridec-. Fourteen is tetradec-. A tetrapod is something
with four legs. And after that it, becomes
very systematic. At fifteen is pentadec-. Notice pent-, 5 and 10. Sixteen is hexadec-. Seventeen is heptadec-. So it just goes on
and on and on. I don’t think I’ve got to go–
anyway, it’s hexadec-, heptadec-, octodec- is
eighteen, nineteen is nonadec-, and then twenty
is actually iso-. But we won’t even
go into that. This’ll probably serve
our purposes. I mean, I could go up to
sixteen is hexadec-. So this is just how
many carbons are in our longest chain. What I drew here is
just one chain. So we could immediately–
let’s try to name it. Well, how many carbons
do we have here? Well, we have one, two, three,
four, five, six carbons. So we’ll be dealing with
hex- as a prefix. And then to get, I guess, the
post-fix on this prefix, or the kind of the root, you look
to see if there are any double bonds here. And there are no double
bonds here. And if we have no double bonds
in this carbon chain, we’re dealing with an alkane. This is called an alkane, which
is a general term for all of the chains of carbons
that have no double bonds on them, or no triple bonds,
all single bonds. So in this situation, you take
hex- for six, so this is hex-. And then, because it’s
an alkane, it gets the -ane from alkane. So this is hex-,
this is hexane. Let’s do another one. Let’s say I have this
thing right here. I’ll draw– let’s make
it even longer. So let’s say I have that
thing right there. So how many carbons
do we have? We have one, two, three, four,
five, six, seven carbons. They’re all single bonds,
so it’s an alkane. So this will be seven carbons. It is heptane because we
have all single bonds. Now, if things form a chain,
or if things form a ring, I should say, we put the prefix
cyclo- in front of it. So if I have– let me show you
what I’m talking about. So if I just have five carbons,
one, two, three, four, so one, two, three,
four, five. OK, so that’s five
right there. I have one, two, three, four,
five carbons in a chain. If I just have five carbons in
a chain like this, this would be pentane. But if I have five carbons
and they form a ring, so let me draw it. So it’s one, two, three,
four, five carbons and it forms a ring. Let me make the drawing
a little bit better. So it’s really, I’m just
drawing a pentagon. But notice, this has
five carbons on it. I can draw the carbons here. Carbon, carbon, carbon,
carbon, carbon. And just as a review, what you
don’t see is the hydrogens they’re bonded to. Each of these guys have two
bonds, so they must have two bonds with something else and
those are going to be with hydrogen, And I’lll draw it here just as
a bit of a review, but you notice very quickly, the drawing
gets extremely messy when you draw the
two hydrogens on each of these carbons. So it’s a little bit
over– maybe I shouldn’t be doing that. But there you go. So it becomes very messy when
you draw the hydrogens, so it’s better to just assume
that they’re there. If we don’t draw all four bonds
of the carbon, the other two bonds are going to
be with hydrogen. So here, you might say, OK, this
is an alkane, because I don’t have any double
bonds here. All of these are single
bonds with the carbon. I have five carbons, so you
might say this is pentane, but you have to think about
one more thing. It’s in a ring, so we add
the prefix cyclo- to it. So this is, because it’s a ring,
we write cyclopentane. So let me just break
that apart. This tells us that we’re
dealing with a ring. You see that this is
a ring right there. This tells us that we’re dealing
with five carbons, and then this tells us right here,
the -ane part, that tells us that they are all
single bonds. All carbon-carbon
single bonds. No double or triple bonds. All single bonds. So let’s go the other way. Let’s start with the word and
let’s see if we can figure out what the actual structure
would look like. Let’s say I have cyclononane. So what is this telling me? This tells me I’m dealing
with a ring. That is a ring. It’s going to have
a ring structure. It’s going to have nine carbons,
nine C’s, and then it’s an alkane, so they’re all
going to be single bonds. So if I want to draw it, I want
to draw nine carbons in a ring, it’s not a trivial
thing to draw. I’ll try my best, so let’s see,
that’s one, two, three, four, five, six, seven, eight. Let’s see, let me draw it. I’ll try a little a
better shot at it. So, let’s see, you have one,
two, three, four, five, six, seven, eight, and then nine. And then you can connect the
last. So let me make sure that this is– and obviously, I could
have drawn it better than that, but hopefully, you
can see all of the edges here. So I have one, two, three, four,
five, six, seven, eight, nine carbons. It’s in a cycle. It’s in a ring. I have nine carbons. They’re all single bonded, so
this is cyclononane, although there’s probably better ways to
draw that ring right there. So if someone were to tell you,
octane, and that word might feel familiar to you
from the gas station. They are literally talking about
the molecule octane. And now you know, or at least
you have a sense of what they’re talking about. The oct- tells you that you
have eight carbons. There’s no cyclo- in front of
it, so it’s not a cyclo. It’s just going to be a chain. And then the -ane part tells
you that they’re all single bonds, so it’s just going to be
eight carbons in a chain. One, two, three, four, five,
six, seven, eight. It’s just going to
look like that. One, two, three, four, five,
six, seven, eight. In the next few videos, we’ll
add more to these molecules and make the names even
more complex.

100 Replies to “Naming simple alkanes | Organic chemistry | Khan Academy”

  1. The methyl group is responsible for the potentiation of effects as compared to the related compound amphetamine, rendering the substance more lipid-soluble, enhancing transport across the blood–brain barrier, and more stable against enzymatic degradation by monoamine oxidase (MAO).

  2. Our teacher sets these videos as homework and sometimes just plays them to the class 😀

    Thanks from Australia 😀

  3. Egad, I need more hours in the day! I just came across Biomimicry. Last week all I could think about was Energy. Oh yeah an something called Rsa which is a drawing that explains something so you understand it. Whew! Maybe i need to try Decaf?
    Is it true? Did the IRS layoff its workers?

  4. actually the prefixes from pent- , hex- etc ,come from the greek words for numbers,5=pente,6=hexi,7=hepta etc :). Great vid btw. thanks:))

  5. I'm reviewing in advance for next semester and honestly, I couldn't understand my book references in Organic Chem. Thanks Khan Academy!

  6. These tutorials make my advanced organic chemistry book look like a piece of cake! Thanks for the simple but effective explanations!!

  7. I dig everything. the ease. the pep. your voice. hell yes dude. I have 2 more nights to study for my next organic exam and you have renewed my hope after a rough 8 hour study session tonight. I'll be watching plenty of your videos

  8. Some of my students used these videos to supplement the class materials I was confused as to why names were being capitalized and when asked to draw the isomer of octane present in gasoline (2,2,4-trimethylpentane) the students drew the structure of octane.  Each of the students told me they had watched this video.  1.  names of chemical compounds are common nouns and should not be capitalized unless at the beginning of a sentence.  2.  The discussion of octane in gasoline does not refer to octane (n-octane)  It is referring to isooctane or 2,2,4-trimethylpentane (an isomer of octane as it has the formula C8H18).  Other than those 2 issues, the video is not bad.

  9. thanks ….. 
    but we need some practical laboratories that uploaded to your channel ….. we need it for deep understand ….. regards 

  10. Whoever believes in the Son has eternal life, but whoever rejects the Son will not see life, for God's wrath remains on him” (John 3:36).

  11. Revelation 14:9-11
    And another angel, a third, followed them, saying with a loud voice, “If anyone worships the beast and its image and receives a mark on his forehead or on his hand, he also will drink the wine of God's wrath, poured full strength into the cup of his anger, and he will be tormented with fire and sulfur in the presence of the holy angels and in the presence of the Lamb. And the smoke of their torment goes up forever and ever, and they have no rest, day or night, these worshipers of the beast and its image, and whoever receives the mark of its name.”

  12. Exodus 20:4-5

    “You shall not make for yourself a carved image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth. You shall not bow down to them or serve them, for I the Lord your God am a jealous God, visiting the iniquity of the fathers on the children to the third and the fourth generation of those who hate me,

  13. This stuff made no sense to me when my professor taught it, the book confused me even more – thank you so much for making this super simple. NOW I understand what the professor and the book were trying to say. Both seemed to skip over these fundamental basics. I believe you just saved my next chemistry exam score lol

  14. haha thanks for saving my life! i missed 30 minutes of class and pretty much skipped the WHOLE lesson which i basically really needed..

  15. This video's been on youtube for 7 years and has less than a million views. Someone posts a lets play video and gets 5 million views in a week. Sad.

    I watched this series 5 years ago and it gave me enough knowledge where I'm no longer confused about organic chemistry and I can understand molecule diagrams on wikipedia. Invaluable.

  16. sir it make very easy to understand the ch so very very thankfully to you sir some people offer me a app that is TOPPR name app that is same of u but only one difference is there I that app it is when we have some problem related with study I can chat and discus about that with the any teacher the best of INDIA so this is the difference in between your app and that app so u try to make for discussing with any best of your teacher please sir I requested I am from INDIA I wish that you will do this for us thank you sir

  17. Sal !! You are SO damn good! Give me a thumbs up if you agree. I've also
    been creating educational content on my channel. I hope you guys will
    support me by watching my videos! Have an amazing day 🙂

  18. why cyclopentane has only 10 hydrogens ? for alkane it should be 12 hydrogens when carbon number is 5 based on the formula cnh2n+2….

  19. 'M'onkey 'E'at 'P'eeled 'B'anana 'P'lease 'H'and 'H'im 'O'ne 'N'inth 'D'ivision
    M Methane
    E Ethane
    P Propane
    B Butane
    P Pentane
    H Hexane
    H Heptane
    O Octane
    N Nonane
    D Decane

  20. (before watching the video) my teacher taught this and majority of the class dont get it yet and im one of those (i actually get it but i get confuse sometimes and that leads me to making mistakes on recitations/activities thats why i need help) but i can feel the upcoming activities/seatworks/tests based on organic chemistry next week so im here doing self study.. i rlly hope i will be able to get this by now ><

  21. I slept in class and thanks dude, you just helped me out. Otherwise my lifetime streak of not failing in any exams would be over. It's bigger than Goldberg's 173-0.

  22. This makes so much sense! Thank you! Side note: When you started talking about "Cyclo" I thought about Cyclobenzaprine and a lightbulb went off in my head!

  23. Its sad people pay thousands upon thousands of dollars for college to have to come to a youtube to learn this.

  24. Sir plz reply? Is it right to number to that side of chain where smaller radicle is present if two defferent alkyl radicles are present at same postition in the chain

  25. Why am I paying my college $3k per semester just so I can come to youtube to do the actual A) Learning & B) Unconfusing done at school.

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