Organic Chemistry 2 - Chapters 14-23 Review

Flashcards covering conjugated compounds, benzene, aromaticity, reactions, and spectroscopic analysis

What distinguishes conjugated dienes from isolated dienes?

Conjugated dienes have two double bonds separated by only a single bond, resulting in different properties due to 2p/2p overlap allowing electron movement across four carbon atoms.

What is required for conjugation to occur?

Conjugation requires p orbitals to overlap on three or more adjacent atoms, allowing for electron delocalization which lowers the molecule's energy and increases stability.

Why is an allylic carbocation considered a conjugated system?

Because it has three or more p orbitals on adjacent atoms, allowing the p orbitals to overlap and electrons to delocalize.

What does the 's' nomenclature stand for in the context of conjugated dienes?

The 's' stands for 'single', referring to stereochemistry about the single bond of the diene, leading to s-trans and s-cis conformations.

What stabilizes the allyl carbocation?

Conjugation, more specifically, delocalization stabilizes the charge in the allyl carbocation.

What are the key characteristics of resonance structures?

Resonance structures differ in the location of the double bond, and either the charge, the radical, or the lone pair.

What happens when a mixture containing predominantly the 1,2-product is heated?

The 1,4-addition product becomes the major product at equilibrium.

What are kinetic and thermodynamic products?

The kinetic product is formed faster and predominates at low temperature; the thermodynamic product is more stable and predominates at equilibrium.

What happens in the Diels-Alder reaction?

A ring-forming reaction takes place between a conjugated diene and an alkene (dienophile) to produce a cyclohexene.

List the key rules for the Diels-Alder reaction.

1. Diene must be in s-cis conformation. 2. Electron-withdrawing substituents in the dienophile increase the reaction rate. 3. Stereochemistry of the dienophile is retained.

What is a fused ring system?

A bicyclic system in which two rings share a common C—C bond.

What is a bridged ring system?

A bicyclic ring system in which the two rings share nonadjacent carbon atoms.

What is the preferred orientation in Diels-Alder reactions?

The endo product is preferred due to more interaction between the electron-rich diene and the electron-withdrawing substituent on the dienophile.

What are the key properties of benzene that must be accounted for in its structure?

It contains a six-membered ring, three additional degrees of unsaturation, is planar, and all C—C bond lengths are equal.

If benzene is a substituent, what is it called?

It is called the phenyl group and can be abbreviated as “Ph-“.

What are aryl groups?

Any substituent derived from aromatic rings.

List the four rules for aromaticity.

1. Compound must contain 4n + 2 p electrons. 2. Compound must be cyclic. 3. Compound must be planar. 4. Compound must have p orbitals on all atoms in the cyclic ring.

What is an antiaromatic compound?

If a molecule contains 4n p electrons, then the molecule is antiaromatic.

What is a heterobenzene?

In organic chemistry, all atoms except carbon are called heteroatoms and so a heterobenzene is when a CH unit of benzene is replaced with a heteroatom like nitrogen creating pyridine.

What is the characteristic reaction of benzene?

Electrophilic aromatic substitution (SEAr), in which a hydrogen atom is replaced by an electrophile.

What are the general steps for electrophilic aromatic substitution (SEAr)?

First, the electrophile, E+, adds to the aromatic ring to form a resonance-stabilised carbocation, and then deprotonation with a base allows the ring to regain its aromaticity.

Why is a catalyst (like FeBr3 or FeCl3) needed for the halogenation of benzene?

Halogens themselves are not strong enough electrophiles (Lewis Acids) to react with the weakly nucleophilic benzene. The catalyst converts the halogen to a stronger Lewis acid.

What is Friedel-Crafts alkylation?

An electrophilic aromatic substitution reaction that attaches an alkyl group to the aromatic ring.

What are the limitations of Friedel-Crafts alkylation reactions?

1. Reactions are limited to alkyl halides. Aryl and vinylic halides do not react. 2. Polyalkylation is often observed. 3. Poor yields are obtained if the aromatic ring contains a deactiving group. 4. Carbocation rearrangements often occur.

What is Friedel-Crafts acylation?

This reaction places an acyl group (RC=O) onto an aromatic ring.

How can Friedel-Crafts acylation be used instead of Friedel-Crafts alkylation?

There is no poly-substitution in Friedel-Crafts acylation and so it can be used often instead of Friedel-Crafts alkylation to make single desired alkylated aromatic rings.

What are electron-donating groups?

Alkyl groups or groups with a N or O atom (with a lone pair) bonded directly to the ring. They increase electron density in the ring.

What are electron-withdrawing groups?

Halogens or groups with an atom Y bearing a positive charge or partially positive charge (+ or d+) bonded directly to the ring, decreasing electron density in the ring.

What is a benzylic carbon/position?

The carbon adjacent to a benzene ring.

What is retrosynthesis?

The process of working backward from the final desired product to determine the starting materials and reaction sequence for a synthesis.

What must be present to have oxidation at the benzylic position?

There has to be at least one benzylic hydrogen.

What information do Infrared Spectrometry (IR) provide?

Information about functional groups present in a molecule.

What does the Mass Spectrometry (MS) information provide?

Confirm the identity and help in purity determination. It is used together with other analytical methods such as NMR.

What information does Nuclear Magnetic Resonance (NMR) Spectrometry provide?

Powerful analytical technique used to characterise organic molecules by identifying C—H frameworks withing molecules.

What does a non-zero spin mean for the NMR phenomenon?

A non-zero spin is a requirement for the NMR phenomenon

In 1H NMR, what does TMS stand for and what is it used for?

Tetramethylsilane. Standard chosen as it shows a sharp signal at a frequency somewhat removed from resonance frequencies of hydrogens in typical organic molecules and defined as the zero point of the ppm scale.

How do protons in different environments differ in NMR?

Protons in different environments absorb at slightly different frequencies, so they are distinguishable by NMR.

In NMR, what information do intensity of signals provide?

Indicates the relative amounts (how many) of each kind of hydrogen in the molecule. The Integral.

What are homotopic, enantiotopic and diastereotopic hydrogens?

-Homotopic: two hydrogens on the same carbon, where replacing either with X gives the same result.
-Enantiotopic: two hydrogens on the same carbon, where replacing either with X gives enantiomers.
-Diastereotopic: two hydrogens on the same carbon that are chemically different and will have two different signals-replacing either with X will yield disatereomers.

What is spin-spin splitting?

Occurs only between nonequivalent protons on the same carbon or adjacent carbons.

In NMR, what does The (n + 1) rule indicate?

The net magnetic field experienced by a H is significantly modified by adjacent (vicinal) hydrogens.

What is the coupling constant (J) in NMR?

The splitting between the lines.

For which molecule must we know stereoisomers are which could limit a type of reaction?

Wittig Reaction

What influences substitution on a benzylic alcohol?

The Carbonyl Functional Group The carbonyl group is characteristic of both aldehydes and ketones and carboxylic acids and their derivatives, where a carbon is double bonded to an oxygen atom and single bonded to two other atoms.

How are alcohols classified?

Primary, secondary, or tertiary depending on the number of organic groups bonded to the carbon that has the alcohol functional group on it.

What property do the alcohols have that makes them very versatile?

They can act both as acids (Brønsted/Lewis) and Lewis bases (Nucleophiles).

What is the product of the Wittig reaction?

An alkene.

How are amines classified?

1°, 2°, or 3° by the number of alkyl groups bonded to the nitrogen atom.

What product is yielded when an aldehyde or ketone is treated with a primary amine?

An imine (also known as a Schiff base).

What is an enamine?

A compound that results from a 2o amine reactions with an aldehyde or ketone which have a nitrogen atom bonded to a C=C double bond.

What is a hemiacetal?

A compound that forms when a hydroxyl group is part of the same molecule that contains the carbonyl group and a 5- or 6-membered ring can form.

What is a protecting group?

A protecting group for the ketone which makes the reduction of the ester can take place without aCecting the ketone.

What is an alkoxide anion?

unstable unless it’s an aromatic alcohol like phenol anion that results when an alcohol acts as an acid.

Which reagents are used to prepare an alkyl halide on alcohols from alcohols?

H2SO4 or p-toluenesulphonic acid (TsOH).

What must happen for successful oxidation at a benzylic position?

There must be at least one benzylic hydrogen.

What happens with a hydride group that undergoes a planned sp2 hybridized carbonyl carbon to a racemic tetrahedral hybridized carbon?

It has become an achiral group

What is a reaction with acid chlorides?

They are extremely sensitive to the protic solvents such as water, alcohols and carboxylic acids

What group is formed in alcohol oxidation with peroxy acids?

An epoxide

How does acidity change the solubility in carboxylic acids?

The carboxylate salts are often water soluble because they are a product of organic acid reactions

What happens when electron-withdrawing groups stabilize a carboxylate anion?

In general the electron withdrawing groups make the carboxylic acids more acidic

What is contained in a nucleophile as a carboxylic acid?

Removal of the easily removed acidic alcohol acid to allow the carboxylic acid group for attack.

How are nucleophilic acyl substitutions used?

With derivatives to create a negatively charged or neutral group and be able to have a substitution replace the substitution.

What happens with an acid chloride with oxygen nucleophiles?

The acid chlorides React with the oxygen nucleophiles to for an anhydride as a very useful reaction.

Why is the formation of amides so unique?

They occur at high temperatures and is different on other reactions and may not take place because of temperature and composition.

What can help convert OH into a better leaving group?

Use of the conversion through dicyclohexylabodimide (DCC) to stabilize and remove more alcohol groups.

What functional group can peroxy acid reactions provide

Carboxylic Acid (RCOOH)

What happens with organometallics at their carbon-metal bond?

Reagents with polar covalent bonds and reacts like carbanions where M=MG or Li

When is their the reaction on nucleophilic acyl substitution?

Occurs with negatively charged species and neutral but do not provide a base.

Why can a nitrile functional group participate in bonds?

There are three CN bonds which also results in hydrolysis, meaning it can be replaced.

What weak Bronsted compounds are formed with a ketone or aldehyde?

Alpha position of resonance stabilized group

What is formed with Alpha position of resonance stabilized group?

Enolate in order to stabilize from ketone or aldehyde compound

What product group is from B-Dicarbonyl Group?

Carbonyl group and resonance stabilized products

What is are two different pathways occur for in Beta Dicarbonyl Group?

Enolae structures with alpha carbon group

What has to occur for an Enolate structure with alpha Carbonyl Group?

Have proper geometry and hybridization is essential

When should you expect an Enol Structure with geometric stability

Must require and triple bond carbon and a alpha to be stabilized

Which reactions have enols with carbonyl addition?

acid and alpha

For alkate what what type of structure must that bond to?

Ether has to bond with an ester with more stability with ketone.

why do some bonds undergo decarboxylation?

Whenever it can have a better connection with an OH bond.

What type of relationship are stereoisomers?

Alpha stereoisomer and bond to a c carbon

What do you need to produce from dicarbonyl compounds?

Five and six membered carbon to react

What group is important to form, and is produced form that stability?

Aldol and that stability stabilizes enolate

When does the most prominent product form, and and in what way?

Crossed aldol reactions but must minimize base to stay stable.

What does diels produce for ether?

They react by having acidic hydrogens which are extremely important reactants.

Which compound has carbon that is not produced normally?

Michael compounds has beta carbon that is unsaturated.

What is 1-4 addition used?

Stabilize reactions to get an alpha or beta unsaturated.