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here are a few more special alkyl groups, little fragments that dangle off
of parent chains
and so you need to know these by their names when you see them
they are just
very common fragments
and some of the naming
exercises you will
need to use these words this as part of a name for the whole molecule
this next slide shows some examples
that's a three carbon chain hanging off of a nine carbon chain
and since that three carbon chain has the attachment in the middle of those
three carbons that's why it's isopropyl
and the word for the long chains nonane
this one below has a tertiary butyl group a forr carbon branch but that's the carbon
in the middle of that little cluster that's forming the attachment
to that nine carbon chain
again sometimes it's a simple methyl group, sometimes it's
ethyl, sometimes it's isopropyl
a few of these tend to be the very commonly encountered
another aspect in naming is that the carbons don't have to make chains
sometimes they can make rings
and when we draw these
geometric figures like triangles and squares in organic chemistry that refers
to
cycloalkanes
carbons are considered to be at the corners
and they will have
again hydrogens as well
and so the shorthand formulas are used to be even more often than
these other structural formulas
we just have to know that in this class we interpret
the corners to be carbons
and if we needed to add in hydrogens there would be two hydrogens apiece
because in a ring all carbons are connected to other carbons
and therefore would need those two hydrogens
the five and six member rings cyclopentane, cyclohexane those are by far
the most common in nature
and we will see those show up a lot as we go along as well
those rings can have
branches just like a chain can have branches and so as you would guess we
just modify the names in a similar manner
methyl groups hanging off of a ring are
going to have the word methyl in their name just as
they would if they were hanging off of a straight chain
so
at the top we've got a methylcyclopropane
and if we're drawing the ring with just corners to represent carbons then this
little line segment
we assume it ends in a carbon as well so
that's a little stick figure that represents methylcyclopropane
just as we sometimes have to use numbers to locate substituents along chains
we have to do that with the rings sometimes
and so with these two methyl groups hanging off of a cyclohexane ring the
one and the two indicates that they are right next to each other
with a ring in principle it doesn't matter where we would
start numbering our carbons
but certainly we would start if there is a methyl group somewhere and so
no matter which one of these
carbons I label as number one, the other is going to be number two
don't have to necessarily start at the top of the ring, don't have to go
clockwise sometimes in the numbering is backwards counter-clockwise
but we still try to
use the lowest numbers we can get away with
here's a cyclopentane ring--five carbons, and that ethyl group can either
be written as CH2CH3 as it is on the left
or over on the right you can see again we assume that the
corners, the edges of those line segments
as well as the tips are carbons themselves
and although it's not quite as common to use those stick figures with chains
they can be used that way
so we draw zigzag lines we can identify carbons along that chain as
well as carbons that would be on the tips
and for something like decane with ten carbons that's certainly a
handy shortcut
on the left is another way to shorten that formula is to write the CH2
with the eight outside to imply eight
CH2 groups all in sequence
this one at the bottom again can be drawn as a stick figure like on
the right
or it can be drawn like you see on the left
and that it's named as a pentane
because up here on the top
left corner that's not really part of the branch that's really the first
carbon in five in a row
because if I start counting there I can identify this CH3 as the first carbon
in the chain
and then go two three
four and five
and these two methyl groups hanging here down towards the bottom are branches off
of that
parent chain