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42 Cards in this Set

  • Front
  • Back
What are Bronsted Acids and Bases?
Bronsted Acid - tendency to lose a proton, (H)
Bronsted Bases - tendency to accept a proton, (H)
If the value of delta G is very negative, in which direction is equilibrium favored?
Large delta G ~ equilibrium lies well over to the right
What is a zwitterion? Draw and example.
A zwitterion is a neutral species that contains goth a positive and a negative charge.

Ex.: B-15
What is the pH a measure of in a solution?
pH is a measure of the acididty of a solution.
What is the equation relating pH and H3O+?
pH = -log[H3O+]

(pKa = -log[Ka])
What is the equation frot he ionization constant in water?
Kw = [H3O+][OH-] = 10^-14 mol^2dm^-6
For a strong acid in an aqueous solution, does equilibrium lie to the left or to the right?
In a mixture of acid in an aqueous solution, what happens to the solubility as pH is lowered? How does this relate to aspirin in the stomach?
pH is lowered ~ acidic for present increases ~solubility decreases

In the acidic environment of hte stomach, soluble aspirin is converted back to the normal acidic form and precipitates out of solution.
What is the equation that relates pH and pKa?
pH = pKa + log([A-]/[AH])
Acids are dissolved by raising/lowering pH; bases are dissolved by raising/lowering pH.
Acids are dissolved by raising pH. Bases are dissolved by lowering pH.
Using the relationship between solubility and pH, how can organic acids be separated from mixtures of other compounds?
Dissolve the mixture of compounds in dichloromethane, (which is immiscible with water ~separates into different layer),a nd 'wah'this solution with aqueous sodium hydroxide, any organic acids present will be converte do their water-soluble wsalts and sissolve into the water layer.
Is anionic A- more or less soluble in water than a neutral acid?
A- is more soluble
Is a netural acid more or less soluble in organic solvents than anionic A-?
Neutral acids are more soluble - the more neutral, the closer to organic solvents ~ the more soluble
Is a cationic acid, (HB+), more or less table in water than the neutral conjugate base B?
HB+ is more soluble
Is a neutral conjugate base, (B), more or less soluble in organic solvents than the cationic acid, (HB+)
Neutral conjugate base is more soluble
What does an acid's pKa depend on?
Acid's pKa depends on the stability of its conjugate base.
The stronger the acid, the stronger/weaker its conjugate base?
The stronger the acid, the weaker its conjugate base.
Why does a stronger acid have a weaker conjugate base?
The stronger acid wats to give of its H, so it does not want to take the H back when it has become a conjugate base.
Why does a weaker acid have a stronger conjugate base?
A weak acid does not want to give off its H as readily, so it wants to take the H back when it has become a conjugate base.
What does the ratio of pKa values tell us?
Give an indication of the equilibirium constant for the reaction bewteen a base and an acid.
What does the difference in pKas tell us?
Give the log of the equilibirum constant.
What is the strongest base in aqueous solution?
What is the strongest acid in aqueous solution?
What happens to the concentration of OH- in an aqueous solution when a stronger base is added?
Concentratin of OH- increases, because more water molecules are deprotonated.
What happens to the concentration of H3O+ in an aqueous solution when a stronger acid is added?
Concentratin of H3O+ increases, because more water molecules are protonated.
As conjugate bases become more stable, do they become more or less basic?
Less basic

(The more stable the conjugate ~ the less basic it is ~ the stronger the acid that yields it)
As elements become more electronegative, do they tend to have more or less stable conjugate bases?
The more electrognegative the element, the more stable the conjugate base.
Are electrons in an sp-orbital higher or lower in energy than those in an sp^2 orbital
sp is lower than sp^2, (which is lower than sp^3)B
What is the order of stability of anions derived from alkanes, alkenes, and alkynes.
Anions from alkynes are more stable than those from alkenes, which are more stable than those from alkanes
If pKa is higher, is it more or less stable?
More stable ~higher pKa
What are 5 ways to stabilize the conjugate base, (A-)?
1. Have the charge on an electronegative element
2. Deloclalizing the negative charge over other carbon atoms, or even better, over more electronegative atoms
3. Spreading out the charge over electron-withdrawing groups by teh poliarization of sigma bonds, (inductive)
4. Having the negative charge in an orbital with more s character
5. Becoming aromatic
Give an equatoin relating pKa, pKb, and pKw.
pKa + pKB = pKw = 14
What are the two main factors that determine thestrength of a neutral base?
1. HOw accessible the lone pair is
- The higher the energy of the HOMO of the molecule, the more reactive it is, so the stronger of a base.
2. To what extent the resultant positive charged form can be stabilized either by delocalization or by the solvent.
- The lone pair is lowered in energy if it is ion a very electronegative element.
As the number of R groups increases, doe shte pKaHs become lower or higher?
What 2 factors does basicity result from?
1. The increased availability of the lone pair and the stabilization of the resultant positive charge, which increases with successive replacement of hydrogen atoms by alkyl groups
2. The stabilization due to solvation, an important part of which is due to hydrogen bonding; this effect decreases with increasing numbers of alkyl groups.
If the lone pair on nitrogen is less available for portonation, is the amine more or less basic?
Less basic
If the electron density on nitrogen decreases, with the amine be more or less basic?
Less basic, because the lone pair is less available for protonation.
What are 4 ways to decrease the electron density on a nitrogen, (thereby making it less basic)?
1. Nitrogen atom is attached to an electron-withdrawing group
2. Long pair is in an sp or sp^2 hybridized orbital
3. Lone pair is conjugated with an electron-withdrawing group
4. Lone pair is involved in maintaining hte aromaticity of the molecule
What is an amidine?
The nitrogen equivalent of an amide, (a C-NH gropu replaces the carbonyl)
What type of bases are amidines?
Among the strongest neutral bases.
The numver of electronegative atoms on which to stabilize positive charge corrleates with what characteristic?
As the # of electronegative atoms on which to stabilize positive charge increases, so does the stability of basicity
What are tautomers?
Isomers differing only in the positions of hydrogen atoms and electrons.