Naming Alkenes, IUPAC Nomenclature Practice, Substituent, E Z System, Cycloalkenes Organic Chemistry

The Organic Chemistry Tutor

1 Dec 201616:55

EducationalLearning

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TLDRIn this video, the nomenclature of alkenes is explained, covering cis and trans isomers, and the E/Z naming system. Starting with the basics, the video explains how to name alkenes based on carbon chain length and the position of double bonds. It delves into more complex naming conventions, including cycloalkenes and multiple double bonds. The video also explains how to determine the priority of substituents for E/Z isomerism, providing clear examples and detailed steps for accurate naming of alkenes.

Takeaways

🧪 Alkene Nomenclature: The script covers the basics of naming alkenes, including the common names for alkanes and how to apply them to alkenes with double bonds.
📐 Cis-Trans Isomers: It explains the concept of cis and trans isomers, which are different forms of alkenes due to the restricted rotation around the double bond.
🔢 Lower Numbering: When naming alkenes, the direction of numbering should be chosen to give the double bond the lowest possible number.
🔡 Suffixes and Prefixes: The script discusses the use of prefixes for substituents (e.g., methyl) and suffixes for the number of double bonds (e.g., -ene, -diene, -triene, -tetraene).
⚙️ Commas and Dashes: The correct use of commas to separate positions of double bonds and dashes to separate numbers and letters in the naming of alkenes is highlighted.
🔄 Double Bond Priority: In the naming process, the position of double bonds takes priority over other substituents.
🔄 Cycloalkenes: The script mentions the naming of cycloalkenes, where the double bond is assumed to be on the first carbon unless specified otherwise.
🔄 E/Z Isomerism: The E/Z system is introduced for naming alkenes with multiple substituents, based on the relative positions of the highest priority groups.
🌐 Stereochemistry: The script explains how to determine the stereochemistry of alkenes, differentiating between E (trans-like) and Z (cis-like) isomers.
📝 ENZ System: For complex alkenes with multiple substituents, the script details the use of the ENZ system for naming, which involves comparing atomic numbers to determine group priority.
🔍 Longest Chain Identification: It emphasizes the importance of identifying the longest chain in a molecule and including the double bond within it for proper naming.

Q & A

What is the basic nomenclature for naming alkenes?
-The basic nomenclature for alkenes involves identifying the longest carbon chain that includes the double bond and assigning numbers to the carbon atoms in a way that gives the double bond the lowest possible number. The name of the alkene is then derived from the corresponding alkane with the suffix '-ene' added.
What are the common names for alkanes from one to ten carbon atoms?
-The common names for alkanes are as follows: methane (1 carbon), ethane (2), propane (3), butane (4), pentane (5), hexane (6), heptane (7), octane (8), nonane (9), and decane (10).
How do you determine the direction for numbering in alkene nomenclature?
-The direction for numbering in alkene nomenclature is chosen such that the double bond receives the lowest possible number. This is done by comparing the carbon atom numbers from both ends of the chain and selecting the direction that results in the lower number for the double bond.
What is the difference between 'cis' and 'trans' isomers in alkenes?
-Cis and trans isomers refer to the spatial arrangement of substituents around a double bond. In cis isomers, the substituents are on the same side of the double bond, while in trans isomers, they are on opposite sides.
What is the ENZ system used for in alkene nomenclature?
-The ENZ system is used for naming alkenes with complex substituents or multiple double bonds. It helps in determining the stereochemistry (E or Z) and the order of substituents based on their priority.
How do you name an alkene with multiple double bonds?
-An alkene with multiple double bonds is named by identifying the longest chain that includes all the double bonds, assigning the lowest numbers possible to the double bonds, and using the suffix '-adiene' for two double bonds, '-atriene' for three, and '-tetraene' for four, etc.
What is the naming convention for cycloalkenes?
-Cycloalkenes are named by adding the suffix '-ene' to the name of the corresponding cycloalkane. If there is only one double bond in the ring, it is automatically assumed to be at carbon one, so the number does not need to be specified.
How do you determine the priority of substituents in the ENZ system?
-In the ENZ system, the priority of substituents is determined by their atomic number, with higher atomic numbers having higher priority. If the substituents are composed of more than one atom, the one with the greater number of atoms or the higher atomic number within the substituent has priority.
What is the difference between 'E' and 'Z' isomers in the ENZ system?
-In the ENZ system, 'E' isomers are similar to trans isomers, where the highest priority groups are on opposite sides of the double bond. 'Z' isomers are similar to cis isomers, where the highest priority groups are on the same side of the double bond.
How do you name an alkene with a substituent and a double bond?
-An alkene with a substituent and a double bond is named by identifying the longest chain that includes the double bond, numbering the chain to give the double bond the lowest number, and then listing the substituents in alphabetical order before the name of the alkane with the suffix '-ene'.

Outlines

00:00

🧪 Basic Nomenclature of Alkenes

This paragraph introduces the basics of alkene nomenclature, starting with the common names of alkanes from one to ten, such as methane, ethane, propane, and so on. It then explains how to name alkenes by counting carbon atoms and identifying the position of the double bond, using 'ene' as a suffix. Examples are given to illustrate the process, such as naming butene and pentene, and the importance of choosing the lowest numbers when identifying the position of the double bond is emphasized.

05:02

🔍 Advanced Alkene Nomenclature and Isomers

The second paragraph delves into more complex alkene nomenclature, including the naming of alkenes with multiple double bonds (dienes, trienes, etc.) and the use of commas and hyphens in the names. It also introduces the concept of cycloalkenes and how to name them, with a focus on the priority of the double bond in the naming process. Additionally, the paragraph discusses cis-trans isomers, explaining the difference between trans-2-pentene and cis-2-pentene due to the orientation of hydrogen atoms relative to the double bond.

10:04

📚 The E/Z System for Alkene Nomenclature

This paragraph explains the E/Z system for naming alkenes with more than one substituent on the double bond, which cannot be easily described as cis or trans. It outlines the process of determining the E (trans-like) or Z (cis-like) configuration based on the priority of substituents, using atomic numbers and the length of the carbon chain. Examples are provided to demonstrate how to identify the highest priority groups and apply the E/Z prefixes to the alkene names, such as 'Z-2-bromo-2-butene'.

15:05

🔬 Complex Alkene Nomenclature with Multiple Double Bonds

The final paragraph tackles the nomenclature of complex alkenes with multiple double bonds, emphasizing the need to specify the stereochemistry of each double bond with the E/Z notation. It provides a step-by-step guide on how to identify the longest carbon chain, assign the lowest numbers to the double bonds, and use the E/Z system in conjunction with the substituents' alphabetical order. A detailed example concludes the paragraph, demonstrating the complete nomenclature process for an alkene with two double bonds and various substituents, resulting in a name like '3-chloro-6-methyl-2,5-octa-1,3-dien-8-yne'.

Mindmap

Keywords

💡Alkenes

Alkenes are a class of hydrocarbons that contain at least one carbon-carbon double bond. They are a central topic in the video, which focuses on the nomenclature of these compounds. The script discusses how to name alkenes based on the position of the double bond and the presence of substituents, as seen in examples like 'butene' and 'pentene'.

💡Nomenclature

Nomenclature refers to the set of rules for naming chemical compounds. In the context of the video, it is used to explain the systematic way of naming alkenes, including the selection of the longest carbon chain, the position of the double bond, and the naming of substituents.

💡Cis and Trans Isomers

Cis and trans isomers are stereoisomers of alkenes where the position of the substituents around the double bond differs. The video explains that cis isomers have similar groups on the same side of the double bond, while trans isomers have them on opposite sides, as illustrated by 'cis-2-pentene' and 'trans-2-pentene'.

💡E/Z System

The E/Z system is an alternative method for naming alkenes that involves assigning priorities to the substituents based on their atomic numbers. In the video, it is used to distinguish between alkenes with different stereochemistry, such as 'Z-2-bromo-2-butene', where the highest priority groups are on the same side of the double bond.

💡Double Bond

A double bond in the script refers to a chemical bond between two carbon atoms where they share four electrons. The position and nature of the double bond are crucial in determining the name and properties of alkenes, as seen in the examples of '1-butene' and '2-pentene'.

💡Substituents

Substituents are the atoms or groups of atoms that replace hydrogen atoms in hydrocarbons. In the video, substituents like methyl, ethyl, and halogen atoms are used to modify the names of alkenes, as in '2-methyl-3-hexene' and '7-bromo-1,3,5-cycloheptatriene'.

💡Carbon Chain

The carbon chain is the sequence of carbon atoms in a hydrocarbon molecule. The video explains that the longest continuous chain of carbon atoms is chosen for naming alkenes, and the position of the double bond along this chain determines the numbering, as in 'heptene' and 'octa-2,5-diene'.

💡Cycloalkenes

Cycloalkenes are alkenes that contain a ring of carbon atoms with at least one double bond. The video discusses how to name these compounds, such as 'cyclohexene', where the double bond is assumed to be at the first carbon unless specified otherwise.

💡Suffix

A suffix in chemical nomenclature is a group of letters added at the end of a word to indicate its kind, nature, or function. In the video, suffixes like '-ene' for alkenes and '-adiene' for dienes are used to indicate the presence of double bonds, as in 'buta-1,3-diene'.

💡Halogenated Hydrocarbons

Halogenated hydrocarbons are hydrocarbons in which one or more hydrogen atoms have been replaced by halogen atoms. The video provides examples of such compounds, like '2-bromo-2-butene', where the bromine atom is a substituent in the alkene.

💡Stereochemistry

Stereochemistry is the aspect of chemistry concerned with the three-dimensional arrangement of atoms in molecules. The video discusses stereochemistry in the context of cis-trans isomers and the E/Z system, explaining how the spatial orientation of substituents affects the naming and properties of alkenes.

Highlights

Introduction to nomenclature of alkenes, including cis/trans isomers and E/Z naming system.

Basic alkene nomenclature based on carbon chain length, e.g. butene for 4 carbons.

Selecting the lower number for double bond position in alkene naming.

Naming alkenes with substituents, e.g. 2-methyl-3-hexene.

Handling multiple double bonds with diene, triene, and tetraene suffixes.

Using commas to separate numbers and hyphens to separate numbers and letters in alkene names.

Cycloalkene nomenclature, e.g. cyclohexene for a 6-carbon ring with a double bond.

Assuming double bond on carbon 1 in monocycloalkenes.

Naming alkenes with functional groups like bromine, prioritizing double bond position.

Cis/trans isomerism in alkenes due to restricted rotation around double bonds.

Differentiating cis-2-pentene from trans-2-pentene based on substituent positions.

Using E/Z system for complex alkenes with multiple substituents.

Determining E/Z isomers based on priority of substituents using atomic numbers.

Naming E/Z alkenes with examples like Z-2-bromo-2-butene.

Identifying longest carbon chain and numbering to give double bond lowest number.

Alkene naming with multiple double bonds and substituents, e.g. 3-chloro-6-methyl-2,5-octa-2,5-dien.

Concluding the video with a comprehensive example of alkene nomenclature.

Transcripts

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