Each of the following names is incorrect. Explain why it is incorrect and give the correct IUPAC

Each of the following names is incorrect. Explain why it is...

Key Concepts

Functional Group Priority (e.g., hydroxyl groups)

Certain functional groups, like hydroxyl groups, have higher priority in the IUPAC nomenclature hierarchy. This means they influence how a compound is numbered, often requiring them to have the lowest possible number in the name. When a molecule contains both an unsaturation and a high-priority functional group, the numbering must reflect the priority hierarchy to ensure that the most reactive or defining feature of the molecule is correctly indicated.

Geometric Isomerism (E/Z)

The designation of geometric isomers (E/Z) in alkenes is based on the relative priorities of the groups attached to the double-bonded carbons. Correct application of these descriptors is necessary to convey the precise spatial arrangement, as incorrect assignment can lead to ambiguity about the stereochemistry and, ultimately, the chemical behavior of the compound.

Double Bond Positioning in Alkenes

In naming alkenes, the position of the double bond must be clearly indicated by the lowest numbered carbon atoms involved in the multiple bond. This often takes precedence over other substituents. When the numbering does not start at the end nearest to the double bond, the resulting name may misrepresent the location of the unsaturation, which is a key factor in the compound’s reactivity.

Cycloalkene Naming Conventions

When naming cyclic compounds with double bonds, the numbering of the ring should ensure that the double bond receives the lowest possible locant numbers. Additionally, substituents on the ring must be numbered in a way that adheres to the priority rules, which can differ from those in acyclic systems. Incorrect numbering in cyclic systems can misplace functional groups and distort the intended structure.

Principal Chain Selection and Numbering

Selecting the longest continuous carbon chain that contains the highest-priority functional group(s) is essential. The chain must be numbered in a way that assigns the lowest possible locants to the highest priority groups, such as double bonds or substituents. Incorrect chain selection or numbering leads to names that do not reflect the most chemically significant features of the molecule.

IUPAC Nomenclature Rules

IUPAC rules provide a systematic method for naming organic compounds so that each name uniquely identifies a structure. This includes rules for numbering the carbon chain, naming substituents, indicating unsaturation (double bonds) and stereochemistry, and naming cyclic structures. Following these rules ensures clarity and consistency in communicating chemical structures.

Substituent Prioritization and Locant Assignment

When multiple substituents are present, each must be assigned a locant that reflects its position on the main chain. The numbering should minimize the numbers assigned to these substituents based on their positions. Failing to do so can result in an ordering that contradicts the established conventions, which is why ensuring that substituents receive the lowest possible numbers is critical.

Transcript

00:02 This is the answer to chapter 10, problem number 45 from the smith organic chemistry textbook.

00:10 And this problem says each of the following names is incorrect.

00:15 Explain why it is incorrect and give the correct iupac name.

00:19 Okay, so simple enough, what i've done, and i did this ahead of time to try to cut down on the length of this video, because it would be pretty lengthy otherwise.

00:31 So i've drawn each of these molecules out the way that they're named.

00:37 And what you can see when you draw them out is that there's a better way to name each of these.

00:41 So looking at a, a is two butyl three methyl -methal -1 pentene.

00:46 But when you draw it out, what you see is that if you name the molecule so that that two -butyl group is instead included as the longest chain, you get a, hexane chain instead of a pentane chain.

01:04 So this then becomes two secbutyl one hexene.

01:11 So two secbutyl one hexene.

01:23 And just to clarify, so we're numbering one, two, two, three, four, five, six.

01:32 So that's our hexane chain.

01:34 And then we have a secbuttal substituent on two.

01:37 And remember, we always want to name these so that we can name it as the longest base chain possible.

01:44 So then looking at b, b is given as z 2 -methyl -2 -hexene.

01:51 But of course, that's not possible because both of these methyl groups on the left, the left carbon of this double bond are exactly the same.

02:00 They're both methyl groups.

02:01 So we can't call this e or z.

02:03 So this is just 2 -methyl -2 -hexam.

02:10 Wexene.

02:11 Oops, 2 -methyl -2 hexene.

02:16 Because we can't use an e or z designation if we have symmetrical groups.

02:21 So then looking at c, c was originally named e1 isoproble 1 -butein.

02:29 But hopefully you can see right away that we can name that chain as a hexane chain.

02:38 And so this would become 3e, 2m2.

02:44 Methyl three hexene.

02:46 Two, methyl three hexene.

02:55 And so again, that would be starting here.

02:57 One, two, three, four, five, six.

03:04 We always want to name it as the longest chain possible.

03:09 Okay, so then d is given as five methyl cyclohexene, but we can number this better.

03:17 So if instead we go carbon 1 is here, carbon 2 is here, 3 is here, 4 is here.

03:23 Then this is 4 methyl cyclohexene.

03:26 And we do want substituents to have the lowest number possible...

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