0:03 laya hair from layer four sicom and in
0:05 this video we'll look at how to find our
0:08 nest configurations for chiral centers
0:11 with complex or lengthy substituents you
0:13 can find this entire video series along
0:15 with the stereochemistry practice quiz
0:18 and cheat sheet by visiting my website
0:21 layer for sicom slash chirality at this
0:23 point I'll assume you're comfortable
0:25 with finding RNs configurations for
0:29 symbol molecules and if you're not make
0:30 sure you go back and watch those videos
0:33 before you continue with this one but
0:35 now we want to look at what happens if
0:37 you have longer substituents or the
0:39 different substituents start with the
0:42 same atom to remind you we're ranking
0:44 substituents based on their atomic
0:47 number and this is the guide that I have
0:48 on the cheat sheet to help you remember
0:51 which atoms will outrank which so we
0:53 look at our molecule and determine that
0:56 we're comparing carbon to carbon to
0:58 carbon to carbon we look back at our
1:00 little guide I realize we're just
1:03 comparing carbon how do we figure out
1:05 which substituent will rank higher or
1:07 lower if every single one starts with
1:10 carbon what you have to do in this case
1:13 is go deeper into the molecule and to
1:15 show you how to do that I'm going to
1:17 rewrite each substituent and show you
1:20 how to analyze it here we have the four
1:22 substituents keeping the same color so
1:25 you can tell what's what but before we
1:27 continue I want to point out we're not
1:30 looking at the number of atoms bound
1:33 we're looking at bonds to the atom wait
1:36 isn't that the same thing in most cases
1:39 it is but when you have a PI bond for
1:42 example a double or a triple bond you
1:45 have to imagine every bond as its own
1:47 priority so looking at this aldehyde
1:50 where we have a carbon double bound to
1:53 oxygen that's like having a carbon bound
1:56 to two oxygen atoms then oxygen is going
1:59 to rank twice so I'll rewrite the
2:03 carbonyl as two separate oxygen atoms to
2:04 help you remember that and to help you
2:07 rank the first thing we do is look at
2:09 the atoms directly bound to the chiral
2:11 carbon and compare them but in this case
2:13 every single one is carbon so we
2:16 cancel it out if you cancel it out you
2:18 have to look at what is the one absolute
2:22 highest priority on the atom you just
2:24 cancelled out why do I say on the atom
2:26 because for example we have a sulfur
2:29 here but it's jumping we can't skip the
2:32 carbon we have to instead look at what
2:34 is attached to the carbon that we just
2:36 crossed out in red for the aldehyde we
2:39 have an oxygen for this group we can
2:41 choose any of the two carbon atoms it
2:44 doesn't matter carbon is carbon for the
2:46 green group we have an oxygen and for
2:48 the orange group we have a hydrogen now
2:50 we have something to compare to we're
2:55 comparing oxygen to carbon to oxygen to
2:57 hydrogen hydrogen is always your lowest
3:00 priority and that means carbon to
3:02 hydrogen will be number four or you can
3:04 remember the trick I told you in a
3:06 previous video where if there's no
3:09 hydrogen or deuterium methyl is always
3:11 your lowest priority and we just proved
3:15 it then we have carbon which is out
3:18 ranked by oxygen and since the purple
3:20 and green each have oxygen the entire
3:23 blue substituent is the second lowest
3:24 because it's carbon bound to carbon
3:28 making this monstrosity number three and
3:31 one and two will be between the purple
3:33 and green since they each have one
3:37 oxygen don't forget the purple oxygen is
3:40 really just one bond to oxygen equaling
3:43 the green bond to oxygen so we cancel it
3:46 out and then we look at the next highest
3:49 priority not on the atom we just
3:51 cancelled out but the initial carbon
3:53 atom that we cancel out for all of them
3:55 in the purple group we have another
3:58 oxygen atom as the highest priority
4:00 because the double bound counts twice on
4:04 the green we only have hydrogen as our
4:07 next highest priority oxygen outranks
4:09 hydrogen therefore the aldehyde is
4:12 priority number one outranking the ch2oh
4:16 which is priority number two the rest is
4:18 pretty straightforward cancel out number
4:20 four trace the path from one to two to
4:22 three and since the top goes to the
4:26 right or clockwise this molecule is our
4:28 but what if the atoms are not written
4:31 out so clearly what if instead you're
4:34 given a molecule that looks like this
4:36 here we have a molecule with one chiral
4:39 carbon and coming out of it we have
4:41 three carbon containing substituents a
4:44 phenyl group a cyclohexyl group and an
4:47 isopropyl where's the fourth substituent
4:49 don't forget we have an invisible
4:51 hydrogen going to the back whenever
4:53 you're given skeletal structure and
4:55 there is an invisible hydrogen going to
4:57 the back you should automatically know
4:59 that hydrogen is number four so instead
5:01 of writing hydrogen just put a number
5:03 four towards the back you're going to
5:04 cross it out it's going to be out of
5:06 your way if you're comfortable enough
5:08 with this you can even ignore it
5:10 completely and just look at the three
5:13 you're given rank those three fine Arnaz
5:15 never bothering to draw the hydrogen
5:17 mentally acknowledge it but don't draw
5:20 it so let's take a look at our priority
5:24 we're comparing carbon to carbon to
5:27 carbon they're all the same so we cancel
5:29 them out we have to find the next
5:31 highest priority on the red carbon that
5:33 we cancelled out for the one on the Left
5:36 we have a carbon for the phenyl group we
5:38 have any carbon for the cyclohexyl we
5:41 have a carbon once again they cancel out
5:43 so we don't look at the green carbon
5:45 instead we go back to the red carbon and
5:48 see what is the next highest priority on
5:50 the carbon the isopropyl has another
5:53 carbon the cyclohexyl has another carbon
5:55 the phenyl group has another carbon but
5:58 don't forget the PI bond implies yet
6:01 another bond to carbon but once again
6:04 they all cancel out so we look for the
6:07 next highest priority remember the
6:09 phenyl has a PI bond which means this
6:13 counts as a second carbon the isopropyl
6:15 has an invisible hydrogen the cyclohexyl
6:18 has an invisible hydrogen over there
6:19 because it should have four bonds and
6:22 that means the phenyl group having that
6:24 second carbon due to the PI bond
6:26 outranks the isopropyl and cyclohexyl
6:30 making this group priority number one
6:32 going back to the ice to purple and
6:34 cyclohexyl they both have the hydrogen
6:38 so they cancel out what we do now if we
6:39 cancelled out every sin
6:43 Adam on the initial red carbon is we go
6:45 to the next carbon atom and see what is
6:48 highest priority on it and that means we
6:51 would go to any one of the green carbons
6:53 that we rolled out so further the
6:56 isopropyl will show one of the hydrogen
6:58 atoms that's the highest priority
7:00 because all I have left are hydrogen
7:02 atoms it doesn't matter which one I
7:04 choose so we'll choose any one hydrogen
7:08 atom but for the cyclohexyl the highest
7:10 priority is a carbon in addition to the
7:12 hydrogen atoms with carbon is higher
7:14 priority so that's what we're looking at
7:17 carbon outranks hydrogen making it
7:19 higher in priority we have group number
7:22 one making this the second as group
7:25 number two isopropyl as group number
7:28 three and then we simply cancel out
7:30 number four trace from one to two to
7:34 three and our molecule is our for even
7:37 more practice finding RNs on simple and
7:39 tricky molecules make sure you try the
7:41 stereochemistry quiz posted on my
7:44 website LAIV for sicom slash chirality
7:47 for even more chirality be sure to watch
7:49 the upcoming videos where I show you how
7:52 to find RNs for Fischer projections
7:54 Newman projection cyclohexane and chair
7:57 confirmations and then show you how to
7:59 compare molecules to determine if
8:01 they're the same or if there are named
8:05 humors using a combination of logic this
8:08 swap method and probably never redrawing
8:11 the molecule you can find all this with
8:12 my practice quiz and cheat sheet on my
8:15 website at layer four sicom slash chirality
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