5. Chirality

Enantiomeric Excess

Some more facts about optical activity:

<ul>
	<li>Specific rotation [&#945;] is the rotation that 100% pure enantiomers produce.</li>
	<li>Opposite enantiomer = opposite rotation.</li>
	<li>Racemic:A perfect 1:1 ratio of enantiomers</li>
	<li>Scalemic:A non-1:1 ratio of enantiomers</li>
</ul>

Calculating Enantiomeric Excess and Observed Rotation

When 0.200 g of lactose is dissolved in 10.0 ml of water and placed in a sample cell 10.0 cm in length, the observed rotation is +2&#176;. Calculate the specific rotation of lactose.

How to calculate enantiomeric excess.

Calculate the observed rotation when given the following ratio of enantiomers in solution.&#160;

We can also use these equations to calculate specific and observed rotation when other variables are given to us. Just plug the numbers in! Let&#39;s try a few.&#160;

An optically pure (R)-stereoisomer of a molecule has a specific rotation of &#8211; 20&#176;. What specific rotation would be observed for a mixture of the (R) and (S) stereoisomer where there is an enantiomeric excess equal to (S) 60%.

Calculate the observed rotation of a chiral mixture that contains 65% (S)-stereoisomer where the [&#945;] of pure (S)-stereoisomer = -118.

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

Johnny

Organic Chemistry

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Johnny Betancourt

1. A Review of General Chemistry

2. Molecular Representations

3. Acids and Bases

4. Alkanes and Cycloalkanes

6. Thermodynamics and Kinetics

7. Substitution Reactions

8. Elimination Reactions

9. Alkenes and Alkynes

10. Addition Reactions

11. Radical Reactions

12. Alcohols, Ethers, Epoxides and Thiols

13. Alcohols and Carbonyl Compounds

14. Synthetic Techniques

15. Analytical Techniques:IR, NMR, Mass Spect

16. Conjugated Systems

17. Aromaticity

18. Reactions of Aromatics:EAS and Beyond

19. Aldehydes and Ketones:Nucleophilic Addition

20. Carboxylic Acid Derivatives:NAS

21. Enolate Chemistry:Reactions at the Alpha-Carbon

22. Condensation Chemistry

23. Amines

24. Carbohydrates

25. Phenols

26. Amino Acids, Peptides, and Proteins

27. Transition Metals

[BOOK ORGO] CLUTCH

Stille Reaction

Nucleophilic Addition

Overview of Nucleophilic Addition of Solvents

Alkyne Halogenation

Optical Activity

One of the special features of chiral molecules is that they are able to rotate plane-polarized light. Unfortunately, this means that now professors have an excuse to ask you math problems. Let’s see how this works.&nbsp;

Radical Selectivity

Allylic Bromination

Pi Electrons

EAS:Friedel-Crafts Alkylation Mechanism

Friedel-Crafts Alkyation requires an alkyl halide to complex with a Lewis Acid Catalyst before the reaction can begin.&#160;

Kumada Coupling Reaction

Naming Thiols

Alkyne Hydration

Cope Elimination

Cis vs Trans

Since double bonds and rings can&#8217;t rotate, we need different names for the different arrangements they can create.&#160;

IR Spect:Drawing Spectra

E2 - Cumulative Practice

We just tackled the anti-coplanar requirement for E2 reactions. Now, let&#39;s see if you can draw the correct final products using the same molecules we&#39;ve seen in the past. Good luck!

Ozonolysis

Side-Chain Oxidation

We know that the alkyl group directly attached to benzene is known as an alkyl side-chain. Now, regardless of the length of that side-chain, it can be oxidized to benzoic acid using hot KMnO4. What&#39;s the kicker? There must be at least one benzylic hydrogen.

Frost Circle

Ligands

Alcohol Synthesis

H NMR Table

Carboxylation

Let&#39;s learn a really cool way to make carboxylic acids! Are you ready?

Saponification

When you hear "saponification"just know that this is a base-catalyzed hydrolysis of an ester. The mechanism and final product are slightly different. Let's take a look.&nbsp;

Barrier To Rotation

Sometimes we’ll be asked to actually calculate the amount of energy a Newman Projection “spends” while rotating.&nbsp;

Organic Chemistry Reactions

Now you&#8217;re finally getting ready to start understanding types of chemical reactions. Oh joy!&#160;

Sulfide Oxidation

Leaving Group Conversions - Using HX

Axial vs Equatorial

Instead of being planar, cyclohexane twists into something called a chair conformation&nbsp;to reduce angle and torsional strain.&nbsp; &nbsp;

Beta Hydrogen

Halohydrin

Aromatic Heterocycles

Claisen-Schmidt Condensation

When a crossed aldon contains an enolizable aldehyde and a ketone, one product does predominate. Let&#39;s see which one it is.&#160;

Alkyne Oxidative Cleavage

Thiol Reactions

Monosaccharides - Common Structures

Pentoses and hexoses are highly prevalent in biological systems. You probably only need to know a few of these. Let&#39;s learn some tricks to make them easy to remember &#38; draw out.&#160;

Test 1:Plane of Symmetry

The simplest test for chirality is symmetry. If a molecule has an internal line of symmetry, it is achiral.&nbsp;

Fischer Esterification

Fischer Esterification is also known as&#160;acid-catalyzed esterification. Why is it so important? Because we convert an OH group to an OR group.&#160;

t-Butyl Ether Protecting Groups

1H NMR:Spin-Splitting (N + 1) Rule

Advantages of Friedel-Crafts Acylation

Friedel-Crafts Acylation has several advantages that make it much more synthetically useful than alkylation. There are 3 in particular that I want you to know.&#160;

Moving Functionality

Ring Strain

We can use an instrument called a calorimeter to determine how much potential energy is stored in molecules.&nbsp;

Basicity of Aromatic Heterocycles

Addition of Amine Derivatives

Lewis Structure

Drawing Lewis Structures is something we learned how to do in Gen Chem. Nothing has changed since then, but now since we know about bonding preferences, that makes it a lot easier.&nbsp;

SN1 Reaction

Acid-Base Properties of Amino Acids

Amino acids aren&#39;t always represented as neutral structures. It&#39;s time to represent them appropriately.

At physiological pH (7.4), amino acids exist as zwitterions. Let&#39;s take a deeper look.

Benzyne

Benzene can also undergo Nucleophilic Aromatic Substitution via an Elimination-Addition pathway to make aniline. This mechanism requires the formation of a highly unstable aryne (C6H4) intermediate.&#160;

Free Radical Polymerization

Substitution Comparison

Sonogashira Coupling Reaction

Oxidizing Agent

Functional Groups

We can group millions of different molecules into families of similar functionality.

Alkane Halogenation

Hydrohalogenation

Williamson Ether Synthesis

1H NMR:Number of Signals

Dehydrohalogenation

Solvents

Orbital Diagram:4-atoms- 1,3-butadiene

POCl3 Dehydration

Acylation of Aniline

Since aniline is strongly activated, unwanted reactions can occur. However, we&#39;re in luck because we can avoid this issue. Let&#39;s see how.&#160;

Sharpless Epoxidation

Monosaccharides - Acylation

As mentioned previously, monosaccharides have the ability to react at the &#8211;O position in several different ways. In monosaccharide acylation, base promoted conditions can lead to the formation of&#160;polyester derivatives.&#160;

Baeyer-Villiger Oxidation

Monosaccharides - Cyclization

Nucleophilic addition of the penultimate alcohol to the electrophilic carbonyl carbon leads to cyclization. This is the usual case. In the videos below we will refresh your memory on these terms!

Drawing Newman Projections

As we learned already, we use Newman projections to visualize the rotations of conformers. Now we will learn the steps involved to draw the perfect one.&nbsp;

Annulene

Wave Function

Addition Reaction

Proteins and Amino Acids

What&#39;s a protein? Proteins are polypeptides that have some biological function.

Naming Aldehydes

Monosaccharides - Strong Oxidation (Aldaric Acid)

There is a stronger oxidation out there that exists besides bromine/water, which turns monosaccharides into aldaric acid, but oxidizing both the aldehyde at the top and the bottom alcohol forming a diacid.

Glycoside

We know that monosaccharides have the ability to react at the &#8211;O position in several different ways.&#160;In acidic conditions, monosaccharides can alkylate at the anomeric position to produce o-glycosides.

Mass Spect:Fragmentation

Allylic Halogenation

Alkene Stability

Making Ethers - Acid-Catalyzed Alkoxylation

Wittig Reaction

HOMO LUMO

Monosaccharides - Aldose-Ketose Rearrangement

In basic conditions, monosaccharides will undergo a multitude of tautomerizations and isomerizations. The most profound of these is the ability of aldoses and ketoses to reversibly rearrange.

Orbital Diagram:5-atoms- Allylic Ions

Claisen Condensation

What makes Claisen Condensation stand out? Well, much like aldehydes and ketones, esters&#160;can form enolates. The rest well, is history....

Alkyl Groups

IUPAC naming is awesome because it’s pretty easy to master. But unfortunately there are some non-IUPAC names we need to know for this course. These apply mostly to weird looking substituents. Let's take a look.

Hydroboration

Markovnikov

Nucleophilic Substitution

Synthetic Cheatsheet

EAS:Ortho vs. Para Positions

In general, we refer to the products of an EAS o,p-director as a mixture &#8211; but there are some patterns we can learn.&#160;

Polar Amino Acids

Before we memorize the 20 standard amino acids, let&#39;s devote some time categorizing them into structural and functional categories.&#160;

Drawing Atomic Orbitals

Condensed Structural Formula

What if you want to describe a molecule, but you have nothing but a keyboard? (No fancy pictures or drawings). This is was actually a big dilemma in the chemistry world, which is why we now have condensed structure.&nbsp;

Acidity of Aromatic Hydrocarbons

Diazo Sequence Groups

We&#39;ve learned about blocking groups before with sulfonic acid (SO3H), but now let&#39;s see how we can use a diazo group (N2) to function the same way.&#160;

Leaving Group Conversions - Sulfonyl Chlorides

Calculating Energy Difference Between Chair Conformations

Monosaccharides - Drawing Fischer Projections

In order to best visualize sugars we will be using Fischer projections, devised by Emil Fischer himself. The great thing about using these projections is that it will allow us to easily notice chirality centers.&nbsp;

Equatorial Preference

This is the #1 thing you need to know about cyclohexane. So let’s get right into it.

Making Ethers - Alcohol Condensation

Robinson Annulation

1,5-dicarbonyl compounds generated from the Michael Reaction (enone + enolate) have the ability to undergo intramolecular self-condensation into 6-membered enones. Are you impressed yet?

Structure Determination without Mass Spect

Hofmann Elimination

Transesterification

Acetal Protecting Group

Enamine Alkylation and Acylation

Non-Carbon Chiral Centers

E2 - Anti-Coplanar Requirement

Grignard Reaction

Coordination Complexes

Leaving Groups

Alkyl halides aren't the only type of leaving groups out there. Let's explore some of the other types that exist.&nbsp;

Test 3:Disubstituted Cycloalkanes

Since these molecules come up often in exams, it’s a good idea to just memorize a few simple rules for them.&nbsp;

SN2 Reaction

Reducing Sugars

We already learned that a reaction with Bromine water (weak oxidation) provides high yields of aldonic acid. However, this reaction has a limitation:It does not undergo a visible transformation.

Now, lets learn a couple other reactions that have visual cues and also begin talking about &#34;what is a&#160;reducing sugar&#34;&#160;.&#160;

Cumulative Electrocyclic Problems

Congrats guys, we're almost to the end. But before we finish let's talk cumulatively about thermal and photochemical electrocyclic reactions.&nbsp;

How To Determine Solubility

Only one rule to know here:Like polarity&nbsp;dissolves&nbsp;like polarity.&nbsp;

Organic Chemistry

Enantiomeric Excess

concept

example

example