We've already spent a lot of time
talking about how neat carbon is for
life and for biology and for chemical
reactions so much so that there's a
whole field of organic chemistry devoted
to studying the chemistry of molecules
that involve carbon and one of the
things that carbon - or two of the things
that carbon will often bond with are
itself and with hydrogens so much so
that there's an entire class of
molecules that are only made up of
carbons and hydrogens and we call these
it's a very creative name we call them
hydrocarbons - hydrocarbons and you will
see many many types of pure hydrocarbons
and you'll see many other types of
molecules that at least are partially
hydrocarbons or are based on
hydrocarbons so it's a really
interesting thing to study here's three
examples of hydrocarbons these all have
the prefix eth- in the beginning of them
because they have a chain their longest
chain has two carbons and if you want to
study how to name hydrocarbons or
actually organic compounds in general I
encourage you to look at the organic
chemistry section of Khan Academy where
we go into depth on it but this is just
going to get you just kind of dip our
toe in the water just so we get a little
bit familiar so these all have the
prefix eth- which says our longest
chain of carbon we're gonna have two
carbons over here but then we see that
the ending is different over here we
have ethane and it's it's an ane because
we have a single bond over here this
over here we have an ene and that's
because we have a double bond we have at
least one double bond in that chain that
and the carbon chain is only two carbons
over here and it's ethyne here because we
have a triple bond the general term for
a carbon chain that has no double or
triple bonds is an alkane this is a
specific form of an alkane ethane that
has two carbons if the general form for
carbons that have a double bond that's
an alkene actually let me write these
general terms down so I could write al
alkane alkane is the general term for a
chain of carbons that has no double or
triple bonds and specifically this is
ethane if I were generally here and say
alkene now it's
alkine right over here let's think a
little bit about how this bond effects
effects its shape well here I have a
single bond so it essentially forms two
tetrahedrons with one of the carbons at
each of the centers of those
tetrahedrons for example on the left
hand side here when I when I draw this
bond popping when I draw it like this it
means that it's popping out and when I
draw it like this with these lies that
means it's going into into the screen so
I could draw a tetrahedron that looks
that looks like this that's the base of
it and then the top of it is that this
other carbon and it has it has this
carbon at the center and I could also
draw another tetrahedron that has this
carbon at the center this carbon at its top
and it would look it would look
something it would look something like
it would look something like this so for
at least for this molecule you have the
shape is kind of it looks like these two
tetrahedrons that are kind of
overlapping with each other and because
these carbons are they have a single
bond in between them they these two
tetrahedrons can rotate so they could
rotate they could rotate around they
could rotate around that single bond now
things are a little bit different when
you have a double bond when you have a
double bond like this it actually forces
all of these all of these atoms in this
molecule to be in the same plane so this
right over here this ethane this is
planar this is planar right over here
and these this double bond locks it into
place there's not going to be any
rotation when you have a triple bond not
only are you not going to have any
rotation but it's gonna make the whole
thing it's going to make the whole thing
a linear molecule so when we're talking
about its shape we're talking about
these molecules their conformation how
do they arrange themselves in three
dimensions and if you're curious what
these are ethane is a component of
natural gas most of natural gas is
methane methane is just so if I were to
write methane most of natural gas is
methane which is just one which is just
one carbon bonded to four hydrogens
that's methane right over here this is
most of this is the biggest constituent
of natural
gas but you're going to find a little
bit of ethane in there ethene which is
often known as ethylene this has many
industrial uses but maybe most
interestingly it can be used as a plant
hormone that can be used to ripen fruit
ethyne a lot most commonly known as
acetylene this can be used because it
burns very very hot it can be used to
fuel blowtorches so once again you know
these are they seem similar but there
can be used for very very different
things and I could go all day showing
more and more different types of
hydrocarbons but here's just a little
bit more variety just so we can think
about how they're named and the
different forms they take and these are
just three of the different types of
molecules you might find in the gasoline
that you have in your car and there's
many many more than just these and
that's because you mix them with oxygen
put them in an engine and and and spite
and spark them right that they burn well
there they're good fuels to to power
cars but just so get familiar with the
naming mechanism a little bit more this
is pentane it's an alkane with five
carbons one two three four five carbons
in its longer longest chain that's why
it's called pentane because hydrogens
are all of the other bonds that a
carbons are forming sometimes you'll see
a shorthand where something like a
pentane instead of drawing all the Cs
and Hs it would be drawn like this it
could be drawn like this where you
assume that there's just a carbon at
each of these points over there so you
actually don't have to draw the carbon
and then if you don't see if you don't
if something's not bonded to a carbon it
there's no other atom that is drawn in
that the carbon is bonded to you assume
it's just a bunch of hydrogen so this is
a shorthand for pentane which is exactly
this molecule here and you see it has
this kind of it has this bend shape
because carbon is each of the carbons
are trying to get to that tetrahedral
type of shape now this this is
cyclohexane once again it's an alkane we
have no double bonds here hex- is the
prefix because you have six carbons in
your longest chain one two three or you
could say your cycle in this case 5 6
and the cyclo is because instead of it
just being a instead of it being an open
instead of it just being an open chain
it's connected at the end it forms it
forms actual cycle this over here looks
a little
more complex you see the -ene at the end
and that's because the longest chain has
a double bond right over here and the
but- this is the prefix for four this
means that our longest chain has four
carbons and you see that one two three
four carbons but then on this number two
carbon not only did you have your double
bond there but you also have a methyl
group a methyl group 1 carbon meth- is
the meth is the prefix meth- is the
prefix for one so anyway the goal of
this video is really just to give you a
little bit familiar with with
hydrocarbons and and to think about how
they'll be useful in chemistry and parts
of and and and you'll see many molecules
in biology that have hydrocarbon parts
that have chains of hydrocarbons
attached to them so we can think about
the properties associated with them.