more stable conjugate base
⚖️ACS ORGANIC CHEMISTRY STUDY GUIDE
Organic Acids and Bases for the ACS Exam
Compare conjugate-base stability, pKa, equilibrium direction, inductive effects, and solvent effects for ACS organic chemistry.
8 key ideas8 flashcards5 practice questions
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Equilibrium points toward the weaker acid.
favored side of equilibrium
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
A Brønsted acid donates a proton, while a Brønsted base accepts one.
- 02
Lower pKa means a stronger acid under the stated conditions.
- 03
Acid-base equilibria usually favor the side with the weaker acid and weaker base.
- 04
A conjugate base is stabilized by electronegativity, atom size, electron delocalization, induction, and orbital character.
- 05
Electron-withdrawing groups can stabilize nearby negative charge through sigma bonds.
- 06
The effect of an electron-withdrawing group usually falls as its distance from the charged atom grows.
- 07
Solvent can alter basicity and nucleophilicity by stabilizing ions to different degrees.
- 08
A reaction mechanism begins with the most favorable available acid-base event when a strong acid or base is present.
PART OF THE ACS ORGANIC CHEMISTRY GUIDE
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Open the full ACS Organic Chemistry guide →Two ideas worth correcting now
NOT QUITE
→A strong acid has a high pKa
USE THIS INSTEAD
Stronger acids have lower pKa numbers.
NOT QUITE
→Basicity and nucleophilicity always have the same order
USE THIS INSTEAD
Basicity is an equilibrium property; nucleophilicity is a reaction-rate property affected by solvent and steric size.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What does pKa compare?Show answer ＋
It expresses acid strength on a logarithmic scale; a lower pKa corresponds to a stronger acid.
2Which side does an acid-base equilibrium usually favor?Show answer ＋
The side containing the weaker acid and weaker base.
3Why is a carboxylate ion more stable than an alkoxide?Show answer ＋
Its negative charge is distributed across two oxygens.
4How does electronegativity affect anions across a row?Show answer ＋
A more electronegative atom usually stabilizes negative charge better.
5How does atomic size affect anion stability down a group?Show answer ＋
A larger atom spreads charge across a larger volume and is often more stable.
6What is an inductive effect?Show answer ＋
Electron withdrawal or donation transmitted through sigma bonds.
7Why can terminal alkynes be deprotonated by very strong bases?Show answer ＋
The resulting carbanion is sp hybridized and has more s character than an alkene or alkane carbanion.
8Can a strong base also act as a nucleophile?Show answer ＋
Yes, though steric size, solvent, and substrate affect which reaction wins.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01How can two pKa numbers predict an equilibrium?
The reaction tends toward the acid with the higher pKa; a large pKa gap gives a stronger directional preference.
02Why is phenol more acidic than cyclohexanol?
Phenoxide distributes negative charge into the aromatic ring, while cyclohexoxide keeps it mostly on oxygen.
03Why does adding electron-withdrawing fluorines raise carboxylic acid strength?
Their inductive pull stabilizes the carboxylate conjugate base.
04How can solvent reverse a nucleophilicity trend?
Strong solvation can trap smaller anions more tightly, making a larger anion react faster in a protic solvent.
05Why should proton transfer be checked before substitution?
A strong acid-base pairing may consume the reagent or substrate before a carbon reaction can occur.
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