Chapter 4: Acids and Bases Flashcards by Sean Colebrook

What is a Lewis acid? Lewis base?

Lewis acid is defined as an electronic acceptor in the formation of a covalent bond.

Louis base is defined as an electron donor in the formation of a covalent bond.

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What is a coordinate covalent bond?

When Louis acids and bases interact, they form coordinate covalent bonds.

Coordinate covalent bonds or covalent bonds in which both electrons in the bond came from the same starting atom (the Lewis base).

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What is the Bronsted Lowry definition of an acid and a base?

What’s the difference between a Lewis and BL acid/base?

A BL acid is a species that can donate a proton.

A Bl base is a species that can accept a proton.

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What is an amphoteric species?

Give examples.

An amphoteric species have the ability to act as either BL acids or bases.

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What is Ka?

pKa?

What do they mean?

Ka is the acid dissociation constant which measures the strength of an acid in solution.

pKa is the -log(Ka)

More acidic molecules will have a smaller pKA (or even negative).

pKa<2 is a strong acid which almost always completely dissociate and aqueous solutions.

pKa from 2-20 are weak acids.

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pKa values for common functional groups showing functional group and conjugate bases.

What is the pKa of an alkane, amine, alcohol, water, carboxylic acid, hydronium ion?

What is the trend for bond strength down the periodic table? What does that mean for acidity?

What is the trend for electronegativity on the periodic table? What does that mean for acidity?

What can be said for the acidity of a molecule when the en and bond strength oppose each other?

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What is the trend for bond strength on the periodic table? What does this mean for acidity?

What is the trend for acidity and electronegativity?

As we move down the periodic table, the atoms get larger and therefor the electrons aren’t held as tightly (the electrons have higher energy). If the electrons aren’t held tightly, the hydrogen atoms are lost easier and therefor acidity increases.

Higher electronegativity means higher acidity.

When these two trends oppose each other, bind strength determines the acidity.

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What is the alpha hydrogen? Alpha carbon?

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What are the main functional groups that act as acids?

What are the main functional groups that act as bases?

What does that mean?

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Connector check 4.1

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Almost all reactions in organic chemistry can be divided into one of two groups. What are those groups?

Redox reactions

Nucleophile-electrophile reactions

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What are nucleophiles?

“Nucleus loving” species with either lone pairs or pi bonds that can form new bonds to electrophiles.

Nulcleophilicity and basicity have similar definitions:

GOOD NUCLEOPHILES TEND TO BE GOOD BASES.

However, nucleophilicity is a kinetic property because their strength is based on relative rates of reaction with a common electrophile, and base strength is related to the equilibrium position of a reaction and is therefore a thermodynamic property.

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Thermodynamic or kinetic property:

Nucleophile
Base

Nucleaophiles have kinetic property as their strength is based on relative rates of reaction with a common electrophile.

Bases have thermodynamic property because their strength is related to the equilibrium position of a reaction.

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What is a distinguishing characteristic of nucleophiles?

Keep in mind that pi bonds (the electrons associated with a pi bond) will act as nucleophiles in the presence of a good electrophile.

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Generalized examples of nucleophiles, three kinds

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How is nucleophilicity determined?

Protic solvents protonate the nucleophile, reducing its capacity to attack.

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What is the trend for solvents and halogens and nucleophilicity?

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What happens to nucleophiles in polar solvents?

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Examples of strong, fair, and weak nucleophiles.

Can we use nonpolar solvent in nucleophile electrophile reactions?

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What are electrophiles?

Is methyl carbon a better electrophile than bromomethane?

Is acetone (dimethyl ketone) a better electrophile than trimethyl carbanol?

Defined as electron loving species with a positive charge or positively polarized atom that accepts an electron pair when forming new bonds with a nucleophile.

Brings to mind Lewis acids. Electrophiles will almost always act as Lewis acids (accept electrons).

Positive charge increases elcrophilicity.

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Rank the electrophilicity of carboxylic acid derivatives (ester, amides, anhydrides, carboxylic acids)

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What is a leaving group?

What is a heterolytic reaction?

What compounds make good leaving groups?

What compounds make poor living groups?

Leaving groups are the molecular fragments that retain the electrons after heterolysis.

Heterolytic reactions are essentially the opposite of coordinate covalent bond formation: a bond is broken in both electrons are given to one of the two products. The Best living groups will be able to stabilize the extra electrons.

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What is a nucleophilic substitution reaction?

What are the two kinds?

A nucleophile forms a bond with a substrate carbon and a leaving group leaves.

SN1 and SN2 reactions.

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What is an SN1 reaction?

Example.

SN1 (unimolecular nucleophilic substitution) reactions are a type of nucleophilic substitution reaction that happens in two steps:

Step one: formation of the carbocation.

Step two: nucleophilic attack.

Recalling that a nucleophile forms a bond with a substrate carbon and a leaving group leaves in a nucleophilic substitution reaction.

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Does varied stereochemistry result from an SN1 reaction?

What is an SN2 reaction? Example.

SN2 (bimolecular nucleophilic substitution) reactions are a type of nucleophilic substitution reaction in which the reaction contains only one step (a concerted reaction): The nucleophile attacks the compound at the same time as the leaving group leaves.

Why are SN2 reactions considered concerted? Why are they considered biomolecular? Why do less substituted carbons more reactive in SN2 reactions? Speak about the relative stereometric configuration of the product of an SN2 reaction.

Concept check 4.2

The four main determinants of nucleophilicity are: Charge (more negative equals better nucleophile) Electronegativity (more electronegative equals worse nucleophile) Steric hindrance (larger equals worse nucleophile) Solvent (pro solvent, can protonate or hydrogen bond with the nucleophile, decreasing its reactivity)

What is oxidation state? How do you calculate oxidation state? What is the oxidation state of carbon in methane? In formic acid? In CO2? In methanal (formaldehyde)?

Oxidation state is an indicator of the hypothetical charge that atom would have if all bonds were completely ionic. Oxidation state can be calculated from the molecular formula for a molecule. Hydrogen or +1, oxygen are -2, diatomic are neutral, oxidation state of ions (including polyatomic ions) is simply the charge, etc.

What is oxidation? What is reduction? How should we think about oxidation and reduction in organic chemistry and biochemistry?

How can we think about the levels of oxidation of different functional groups?

What is an oxidizing agent? What makes a good oxidizing agent?

How many times can a primary, secondary, and tertiary alcohol be oxidized and what are the products of the oxidation?

What do common oxidizing and reducing agents typically include?

Oxidation reactions and common oxidizing agents. What’s the purpose of this card?

The purpose of this card is not memorization, but recognition of two themes: Oxidation reactions tend to feature an increase in the number of bonds to oxygen Oxidizing agents often contain metals bonded to a large number of oxygen atoms

What are reducing agents? What makes a good reducing agent?

Reduction refers to a decrease in oxidation state. This usually means increasing the number of bonds to hydrogen and decreasing the number of bonds to other carbons, nitrogen, oxygen, or halides.

What can aldehydes and ketones be reduced to? With an amides be reduced to? What can carboxylic acids reduce to? What can esters be reduced to?

Aldehydes and ketones can be reduced to primary alcohols and secondary alcohols respectively. Amides can be reduced to amines. Carboxylic acids can be reduced to primary alcohols Esters can be reduced to a pair of alcohols.

Can carboxylic acids be reduced to aldehydes? Why or why not?

Carboxylic acids cannot be reduced to aldehydes, they are reduced to primary alcohols. Because carboxylic acids have a relatively high oxidation state, a very strong reducing agent needs to be used, which reduces it all the way through the aldehyde stage.

Concept check 4.3 1

Concept check 4.3 2 and 3

Why are aldehydes more readily oxidized than ketones?

Aldehydes are generally more readily oxidized than ketones because of the presence of a hydrogen atom directly attached to the carbonyl carbon in aldehydes. This hydrogen can be readily abstracted by an oxidizing agent, leading to the formation of a carboxylic acid. Ketones, on the other hand, lack this readily abstractable hydrogen, making them more resistant to oxidation under normal conditions.

What is chemoselectivity?

A key skill in recognizing which reactions will occur is recognizing the reactive regions within a molecule. The preferential reaction of one functional group in the presence of other functional groups is termed chemoselectivity.

What is the rule of thumb for reactivity of functional groups?

Which will be the first and last to be targeted by a nucleophile among the following functional groups: Alcohol, amine, ketone, aldehyde, carboxylic acid

Carboxylic acids in their derivatives are the first to be targeted by a nucleophile, followed by an aldehyde, then ketone, followed by an alcohol or amine. Aldehyde are generally more reactive toward nucleophile than ketones because they have less steric hindrance.

Draw a generic keto enol resonance with the enolate formation. Why is this noteworthy?

Within a carbonyl containing compound, the carbon of the carbonyl acquire a positive polarity due to the electronegativity of the oxygen. Thus, the carbonyl carbon becomes electrophilic and can be a target for nucleaophiles. Alpha hydrogen are much more acidic than in a regular CH bond due to the residence stability of the enol form. These enols can be de protonated easily with a strong base, forming an enolate. The enolate then becomes a strong nucleophile, and alkylation can result if good electrophiles are available.

Consider the reactive site of the substrate carbon in substitution reactions. What will SN1 and SN2 reactions prefer?

SN1 (unimolecular substitution reactions) have to overcome the barrier of carbocation stability and therefore prefer tertiary carbons as reactive sites, and secondary to primary. SN2 (bimolecular substitution reactions) have a barrier and steric hindrance. Methyl and primary carbons are preferred over secondary, and tertiary carbons won’t react. This is due to the mechanism of these two reactions shown in the image.

What is steric hindrance? What is steric protection?

Protection of a ketone by conversion to an acetal

What are primary, secondary, tertiary, and quaternary carbons? Use isooctane (2,2,4 trimethyl pentane) as an example.

Concept check 4.4 1,2

Recall that SN1 reactions prefer tertiary over secondary over primary. SN2 reactions prefer methyl over primary over secondary (and do not react with tertiary).

Concept check 4.4 3

Why are SN1 and SN2 reactions named as such?

SN1 and SN2 are named based on the rate-determining step of the nucleophilic substitution reaction mechanism: "SN" stands for "nucleophilic substitution," and the numbers refer to the number of molecules involved in that rate-limiting step. SN1 reactions are unimolecular (only one molecule involved in the rate-limiting step), while SN2 reactions are bimolecular (two molecules involved in the rate-limiting step.

What are the six systematic steps to simplify organic chemistry reactions?

Nomenclature Identify functional groups Identify other reagents Identify the most reactive functional group(s) Identify the first step of the reaction Consider stereospecificity and stereoselectivity

Draw ethyl 5-oxohexanoate and methyl 7-oxobutanoate

-oate is the suffix used for esters. So ethyl-blahblahblah-oate will be an ester on one side of the ester and blahblahblah on the other.

5-oxohexanoate reacted with 1,2 ethanediol and p-toluenesulfonic acid in benzene. Then this is reacted with lithium aluminum hydride and tetrahydrofuran, followed by a heated acidic work up. What are the intermediates and final product? This is a fun one!

Ethanol reacted in acidic solution with potassium dichromate. What do?

Determine the product of a reaction between 2-amino-3-hydroxypropanoic acid and 2,6-diamnohexanoic acid in aqueous solution. Page 118 Awesome fun one. What are alternate names for those two reactants?