Organic Chemistry: Acidity, Basicity, and IR Spectroscopy Review

Flashcards covering lecture notes on organic acidity, basicity, ARIA factors, equilibrium, pH/pKa relationships, Lewis acids/bases, and Infrared Spectroscopy functional group identification.

How does the addition of carbons and branching generally affect the acidity of a molecule?

More carbons and branching increase electron density through the induction effect, leading to destabilization of the conjugate base and making the molecule less acidic.

What is the relationship between the distance of an electronegative group and its inductive effect on acidity?

The closer the electronegative group is to the 'business end' (the acidic proton), the more acidic the molecule will be; the effect is usually negligible after four to six carbons.

What is the approximate pKa of an alcohol?

$15$ to $16$

What is the approximate pKa of a phenol?

$$9$$

According to the lecture, which factor usually trumps others in the ARIA framework (Atom, Resonance, Induction, Orbital) for stabilizing a conjugate base?

Resonance

How does hybridization affect acidity in carbon-based species?

Acidity increases as s-character increases: $SP$ is more acidic than $SP^2$, which is more acidic than $SP^3$.

What is the 'BAD' acronym used for Bronsted-Lowry acid-base theory?

Bases Accept, Acids Donate

What are the three general things to look for when identifying a base?

An anion (negative charge/lone pair), an $SP^3$ neutral nitrogen, or an $SP^2$ neutral nitrogen.

In terms of electron density, what makes a better base?

More electron density (donating groups) stabilizes the lone pair, making it more basic, which is the opposite of acidity rules.

In an acid-base reaction, which direction does the equilibrium favor?

The side of the weaker acid (the side with the higher pKa).

According to the Henderson-Hasselbalch model, what happens when the $pH$ is greater than the $pKa$?

The base form of the species dominates.

Define a Lewis acid and a Lewis base.

A Lewis acid accepts a pair of electrons, while a Lewis base donates a pair of electrons.

In Infrared (IR) Spectroscopy, where does the $SP^3$ carbon-hydrogen stretch appear?

Between $3000$ and $2800\,\text{cm}^{-1}$

What are the two identifying signals for an alkene in an IR spectrum?

An $SP^2$ carbon-hydrogen stretch at $3100-3000\,\text{cm}^{-1}$ and a carbon-carbon double bond ($C=C$) stretch at $1675-1600\,\text{cm}^{-1}$.

How can you distinguish a terminal alkyne from an internal alkyne using IR spectroscopy?

A terminal alkyne shows an $SP$ carbon-hydrogen stretch at $3300-3200\,\text{cm}^{-1}$, whereas an internal alkyne only shows the carbon-carbon triple bond ($C\equiv C$) stretch at $2200-2100\,\text{cm}^{-1}$.

What does a broad peak between $3600$ and $3100\,\text{cm}^{-1}$ indicate in an IR spectrum?

The $O-H$ stretch of an alcohol.

Which two IR signals specifically identify an aldehyde?

The carbonyl ($C=O$) stretch near $1700\,\text{cm}^{-1}$ and two specific $C-H$ stretches at $2800$ and $2700\,\text{cm}^{-1}$.

How do primary and secondary amines differ in their IR spectra?

Primary amines ($NH_2$) show two peaks between $3500$ and $3100\,\text{cm}^{-1}$, while secondary amines ($NH$) show only one peak in that same region.

What is the characteristic IR feature of a carboxylic acid compared to a regular alcohol?

The carboxylic acid has a broad $O-H$ peak that bleeds into the $C-H$ region (near $3000\,\text{cm}^{-1}$) and a strong carbonyl ($C=O$) stretch at approximately $1700\,\text{cm}^{-1}$.