Alkenes, Alkynes, and Alcohols
UNSATURATED HYROCARBONS (ALKENES AND ALKYNES)
Main Idea
An unsaturated hydrocarbon is defined as an organic molecule that contains at least one double bond or triple bond between two carbon atoms.
These types of hydrocarbons can be categorized into two groups based on the type of bond they contain:
Alkenes: Molecules that contain at least one double bond.
Alkynes: Molecules that contain at least one triple bond.
Certain alkenes exhibit a distinctive zigzag shape, leading to the formation of cis and trans isomers.
The double bonds present in alkenes serve as reactive sites, allowing for reactions such as the addition of atoms that can transform the double bond into a single bond.
SKILLS TO MASTER
Identify the correct names for:
Straight chain and cyclic alkenes.
Straight chain and cyclic alkynes.
Identify cis and trans isomers of alkenes.
Predict the products of the following reactions:
Hydrogenation of an alkene.
Halogenation of an alkene.
Hydrohalogenation of an alkene, utilizing Markovnikov’s Rule.
Hydration of an alkene, applying Markovnikov’s Rule.
Classify a molecule as aromatic or non-aromatic.
TERMINOLOGY
Alkene (al-KEEN)
Alkyne (al-KINE)
Aromatic
Benzene (ben-ZEEN)
Cis
Markovnikov’s Rule (mar-KOV-ni-kov)
Trans
ALKENES AND ALKYNES
Naming Steps for Alkenes and Alkynes
Find the longest carbon chain that contains the double or triple bond.
Number the chain starting from the end that is closest to the double or triple bond. This applies regardless of other substituents present.
Locate any substituents and name them in alphabetical order.
Identify the position of the double or triple bond.
Change the ending of the parent chain from -ane to -ene (for double bonds) or -yne (for triple bonds).
CIS-TRANS ISOMERS
Classify each alkene as cis, trans, or neither.
After classification, name as many alkenes as possible.
REACTIONS OF ALKENES
Draw the product of each of the following reactions involving alkenes.
ORGANIC COMPOUNDS THAT CONTAIN OXYGEN, HALOGEN, OR SULFUR
Main Idea
An organic molecule that contains a single-bonded oxygen atom is categorized as:
Alcohol: If the oxygen is located between a carbon and a hydrogen atom.
Ether: If the oxygen is situated between two carbon atoms.
Alcohols are reactive molecules, and the -OH group can undergo transformations.
The removal of the -OH group may yield an alkene, while conversion of the carbon-oxygen single bond to a double bond can create a ketone, aldehyde, or carboxylic acid.
SKILLS TO MASTER
Identify the correct name for straight chain and cyclic alcohols.
Predict the products of the dehydration of an alcohol.
Utilize Zaitsev’s Rule to identify major and minor products during the dehydration of an alcohol.
Predict products of the oxidation of an alcohol, specifically distinguishing between oxidation paths of primary alcohols.
TERMINOLOGY
Alcohol
Dehydration
Ether (EE-thur)
Oxidation
Zaitsev’s Rule (SAYT-sef)
NAMING ALCOHOLS
Steps to Name Alcohols
Find the longest carbon chain that contains the -OH group.
Number the chain starting from the end that is closest to the -OH group, regardless of other substituents.
Identify all substituents and name them in alphabetical order.
Identify the position of the -OH group.
Modify the ending of the parent chain from -ane to -anol.
THE THREE DIMENSIONAL SHAPE OF MOLECULES
Main Idea
Chirality is a property displayed by a carbon atom bonded to four different clusters of atoms.
A chiral molecule and its mirror image resemble a person's left and right hands in connectivity, but they are not identical.
Example: A left glove does not fit perfectly on a right hand, which illustrates molecular chirality.
SKILLS TO MASTER
Determine whether pairs of molecules are constitutional isomers.
Assess if pairs of molecules are stereoisomers.
Locate the chiral carbon (chirality center) in a molecule.
Interpret wedge/dash notation for representing a molecule.
Draw the enantiomer of a molecule.
Convert between wedge/dash notation and a Fischer projection.
TERMINOLOGY
Achiral (aa-KYE-rull)
Chiral (KYE-rull)
Chirality center (kye-RALL-i-tee)
Enantiomer (en-ANT-i-o-mer)
Fischer projection
Stereoisomer
CHIRALITY CENTERS
Identification Tasks
Identify chirality center(s) for each molecule analyzed.
Draw the enantiomer of the following molecules.
Determine the two chirality centers in Zoloft (sertraline).
Identify all four stereoisomers of the molecule and represent their configuration with wedge and dash notation.
Research to confirm which one of the stereoisomers is trademarked as Zoloft.
AROMATIC COMPOUNDS
Definition
An aromatic compound is defined as a molecule containing at least one benzene ring.
Benzene Ring Characteristics
The benzene ring is structured as follows:
Comprises six carbon atoms arranged in a ring.
Displays alternating bonds: double bond, single bond, continuing around the ring.
Different representations for these bonds can exist, and are considered valid.
Shorthand Notation for Benzene Rings
Chemists utilize shorthand notation for a benzene ring represented by:
A six-membered ring with a circle inside for simplicity and expediency.
EXAMPLES OF AROMATIC COMPOUNDS
Pharmaceutical Substances and Natural Products
Example 1: Acetaminophen
Common Name: Active ingredient in Tylenol.
Structure: Contains a benzene ring.
Functionality: Acts as a pain reliever and fever reducer.
Example 2: Vanillin
Description: A natural product that gives vanilla its distinctive fragrance in extracts.
Structure: Includes a benzene ring within its molecular structure.
Summary Note
Numerous aromatic compounds permeate the pharmaceutical and natural products sectors, underlining the significance of benzene rings in chemical contexts.
INTRODUCTION TO THE ALEX PROBLEM
Overview of Task
Focuses on interpreting the skeletal structure featuring aromatic rings in exercises related to the Alex problem.
The primary tasks include:
Generating the molecular formula from a given skeletal structure.
Identifying quantities of CH₃, CH₂, and CH functional groups.
UNDERSTANDING THE BENZENE RING NOTATION
Notation Details
Notation illustrates one six-membered ring with a circle inside, shorthand for benzene that delineates:
Six carbon atoms arranged cyclically with alternating double and single bonds.
Importance of Notation
Understanding this notation aids in simplifying the interpretation of molecular structures.
DETERMINING THE MOLECULAR FORMULA
Step 1: Counting Carbon Atoms
Total carbon atoms measured: C₁₀ (10 carbon atoms).
Step 2: Counting Hydrogen Atoms
General preference of carbon atoms: typically forms four bonds.
Process for counting hydrogen:
Carbon with one bond has three hydrogens.
Carbon with two bonds holds two hydrogens.
A fully bonded carbon has no hydrogens attached.
Overall total counted totals H₁₂ (12 hydrogen atoms).
Final Representation of the Molecular Formula
Complete molecular formula presented as:
C₁₀H₁₂
Notes on Notation
Each element symbol should appear once in the final representation; condensed forms (like CH₃, CH₂) are not acceptable - list totals only.
IDENTIFYING CH₃, CH₂, AND CH GROUPS
Group Count Observations
CH₃ Groups
Analysis shows one CH₃ group present in the structure.
CH₂ Group Count
Evaluation results yield one CH₂ group in the structure.
CH Group Count
Identifying carbons with only one hydrogen: Summation reveals seven CH groups.
Explanation for Accounting
The carbon with no hydrogens does not factor into the count of CH, CH₂, or CH₃.
Summary of Counts
Final summary consists of:
One CH₃ group
One CH₂ group
Seven CH groups
OVERVIEW OF ALCOHOLS
Definition of Alcohols
Alcohols are characterized by the presence of an oxygen atom bonded to one hydrogen atom (-OH) and an additional bond to a carbon atom.
The carbon may have additional bonds, but these do not affect the classification of the alcohol.
The -OH (hydroxyl) group serves as the functional group within alcohols.
Distinction Between Alcohol and Carboxylic Acid
A carboxylic acid contains a carbon-oxygen double bond alongside a hydroxyl group (-OH).
It is crucial to distinguish between alcohols and carboxylic acids:
Carbon in an alcohol retains hydrogens or other carbons, not featuring a carbon-oxygen double bond as seen in carboxylic acids.
NAMING ALCOHOLS
Overview of Naming Process
To effectively name alcohols, foundational nomenclature principles are applied.
Identify the longest carbon chain that contains the -OH group.
Number from the end closest to the -OH group.
Locate and name any substituents in alphabetical order.
Identify the position of the -OH group.
Final Naming: Modify the ending based on the parent structure by replacing -e with -ol.
Practice Examples
Example 1: Identify the longest carbon chain including -OH, number from the closest end, state substituent position, and derive a final name.
Example 2: Identify a cyclic compound's longest chain, numbering and naming appropriately with substituent details.
DEHYDRATION REACTIONS OF ALCOHOLS
Definition and Process
Dehydration Reaction
A dehydration reaction involves an alcohol reacting with a catalyst, commonly sulfuric acid (H₂SO₄).
The reaction encompasses only the alcohol and catalyst, focusing on the hydroxyl group.
Mechanism
The reaction entails the removal of the -OH group from the alcohol along with a hydrogen atom from an adjacent carbon, resulting in the formation of a carbon-carbon double bond.
The omitted hydrogen and the -OH group combine to form water (H₂O).
Example (2-Pentanol)
Reaction Specifications
Reactant: 2-pentanol
Catalyst: H₂SO₄
Drawing the Carbon Skeleton
Structural Outcomes
Potential product combinations arise based on which hydrogen is removed; both will yield different double bond locations.
ZAITSEV'S RULE
Definition
The principal product in the dehydration reaction is identified as the one with the most carbon atoms adjacent to the double bond.
Application: The product with maximum carbon attachment constitutes the major product, while lesser attachments signify the minor product.
INTRODUCTION TO ALCOHOL OXIDATION
Definition of Alcohol Oxidation
Alcohol oxidation refers to reactions that convert alcohols into aldehydes, ketones, or carboxylic acids through the addition of oxygen or removal of hydrogen.
Key Points
The reaction centers around the significance of the carbon-oxygen bond.
Specific Pathways of Alcohol Types
1. Primary Alcohols
Definition: Primary alcohols have the -OH group bonded to the terminal carbon, characterized by the carbon attaching to only one other carbon.
Oxidation Reaction: Typically forms an aldehyde upon oxidation. A stronger oxidizing agent can further oxidize the aldehyde to yield a carboxylic acid.
Reaction: RCH₂OH + [O] → RCHO (Aldehyde)
2. Secondary Alcohols
Definition: Secondary alcohols feature the -OH group on a carbon bonded to two other carbons.
Oxidation Reaction: Yields only one product, a ketone.
Reaction: RCHOH-R' + [O] → RC(=O)R' (Ketone)
3. Tertiary Alcohols
Definition: Tertiary alcohols are those with the -OH group attached to a carbon bonded to three other carbons.
Oxidation Mechanism: Tertiary alcohols do not oxidize due to the lack of adjacent hydrogen atoms needed for conversion to a carbon-oxygen double bond.
ETHANOL OVERVIEW
Definition
Ethanol is the alcohol found in beverages, represented by the chemical formula C₂H₅OH.
Absorption & Distribution
Ethanol is absorbed primarily through the:
Stomach
Small intestine
Transport: After absorption, ethanol enters the bloodstream and affects various organs:
Brain: Alters coordination, mood, memory.
Liver/Kidneys: Major metabolism sites.
Metabolism Pathway
Initial Conversion
Ethanol converts to acetaldehyde through an oxidation reaction, facilitated by the enzyme alcohol dehydrogenase (ADH).
Further Oxidation
Acetaldehyde undergoes subsequent oxidation via aldehyde dehydrogenase (ALDH) to yield a carboxylic acid.
EFFECTS OF ACETALDEHYDE
Hangover Mechanism
Acetaldehyde is recognized as a significant contributor to hangover symptoms:
Symptoms observed include dehydration and stomach lining irritation, which may provoke inflammatory responses due to excessive alcohol consumption.
TREATMENT OF ALCOHOLISM
Medication - Antabuse
Antabuse inhibits the second step of alcohol metabolism, consequently causing a significant hangover upon consumption of alcohol due to the accumulation of acetaldehyde.
Effect: Motivates individuals to reconsider their drinking habits.
METHANOL POISONING
Risks
Methanol is produced during fermentation and may be present in homemade alcoholic beverages, leading to methanol poisoning.
Commonality of Poisoning
Cases of poisoning have occurred with home distillation, necessitating caution during homemade alcohol consumption.
DENATURED ALCOHOL
Definition
Denatured alcohol includes methanol, rendering it undrinkable but suitable for laboratory applications.
Purpose
Allows laboratories to procure ethanol without liquor licenses.
METHANOL METABOLISM
Shared Pathways
Metabolism similarity: Methanol and ethanol utilize the same metabolic pathway facilitated by ADH.
However, methanol metabolism produces toxic formaldehyde, resulting in potential severe consequences such as blindness or coma.
MEDICAL TREATMENTS FOR METHANOL POISONING
Enzyme Inhibitor
Specific medications can inhibit both ADH and ALDH, reducing toxic formaldehyde accumulation.
Ethanol as Antidote
Administering ethanol can promote the preference of ADH for ethanol over methanol, minimizing the conversion of methanol into formaldehyde effectively.
OVERVIEW OF ALCOHOL DEHYDRATION REACTION
Focus
Allows for predicting products resulting from alcohol dehydration reactions.
Type of Reaction
Illustrated as a reaction characterized by the removal of water from an alcohol.
Reagents Used
Typical reagents include:
Proton (H⁺)
Heat (indicated by a triangle symbol)
Mechanism Overview
The hydroxyl group (-OH) is eliminated alongside a hydrogen atom from an adjacent carbon, resulting in a formed double bond between two carbons.
Example Molecule Identification
Trace the structure of the discussed molecule to ascertain carbon atom locations leading to formation results.
DRAWING THE ENANTIOMER OF A SIMPLE ORGANIC MOLECULE
Definition of Enantiomer
An enantiomer is described as a mirror image of a chiral molecule.
Methods to Draw Enantiomers
Method 1: Modifying Bonds
Redraw the original structure, changing wedge bonds to dashed and vice versa while maintaining substituent positions.
Method 2: Drawing the Mirror Image
Utilize a mirror placed adjacent to the structure to visualize its image while preserving the original bond orientation.
CONCLUSION
The properties of chirality and its implications in molecular chemistry are particularly critical in pharmacology and other fields, illustrating the significance of stereochemistry in biological effects and drug interactions.