Infrared Spectroscopy, Mass Spectrometry, NMR, and Carbonyl Chemistry

Flashcards covering the fundamentals of IR, Mass Spectrometry, NMR, and organic reaction mechanisms including substitution, addition, and carbonyl chemistry based on lecture notes.

According to the transcript, what is Planck's constant ($h$)?

$$6.022 \times 10^{-34}\,J \cdot s$$

What is the wavelength range of visible light?

$$400-750\,nm$$

How does electromagnetic radiation interact with a molecule in Infrared (I.R.) spectroscopy?

It interacts with the molecule by causing vibrational excitation (stretching and bending of bonds).

What is the requirement for a molecular vibration to absorb I.R. radiation?

The bond must be polar (only unsymmetrically substituted bonds have dipole moments and are infrared active).

Where is the border between the diagnostic region and the fingerprint region in an I.R. spectrum?

$$1500\,cm^{-1}$$

What I.R. absorption signals are characteristic of an aldehyde?

A strong, sharp carbonyl absorption at $\sim 1720\,cm^{-1}$ and two unique $C-H$ stretches at $2715\,cm^{-1}$ and $2820\,cm^{-1}$.

What does the Nitrogen Rule in mass spectrometry state?

An ODD molecular weight indicates an ODD number of nitrogen atoms; an EVEN molecular weight indicates either the absence of $\text{N}$ or an EVEN number of $\text{N}$ atoms.

What is the formula for the Hydrogen Deficiency Index ($HDI$)?

$$HDI = \frac{1}{2} (2C + 2 + N - H - X)$$

What are the standard chemical shift values ($\delta$) in $^1H$ NMR for methyl, methylene, and methine protons?

Methyl ($R-CH_3$) is $\sim 0.9\,ppm$, methylene ($-CH_2-$) is $\sim 1.2\,ppm$, and methine ($-CH-$) is $\sim 1.7\,ppm$.

In $^{13}C$ NMR, how does the DEPT-135 spectrum distinguish carbon groups?

$CH_3$ and $CH$ groups appear as positive signals, while $CH_2$ groups appear as negative signals.

Why is a conjugated diene more stable than an isolated diene?

This is best explained by Molecular Orbital (MO) Theory and the increased stability from the overlap of four parallel $2p$ orbitals.

In the electrophilic addition of $HBr$ to 1,3-butadiene, which product predominates at $40\,{^\circ}C$?

The $1,4$-adduct, which is the thermodynamic product (more stable).

What are the three requirements for aromaticity specified by Hückel's Rule?

1. A planar ring; 2. Fully conjugated (all atoms are $sp^2$ hybridized); 3. Must have $4n+2$ $\pi$ electrons.

What is the catalyst used for the bromination of benzene in Electrophilic Aromatic Substitution ($EAS$)?

$FeBr_3$ or $AlBr_3$

Which group is a strong deactivator and a meta-director in benzene substitution reactions?

The nitro group ($-NO_2$)

What are the three requirements for Nucleophilic Aromatic Substitution ($S_NAr$)?

1. The ring must contain one or more electron-withdrawing groups; 2. The ring must contain a leaving group ($Cl$, $Br$, $I$); 3. The leaving group must be ortho or para to the electron-withdrawing group.

What reagent is used to oxidize primary alcohols specifically to aldehydes?

$PCC$ (Pyridinium chlorochromate) in $CH_2Cl_2$

In the nucleophilic addition to aldehydes and ketones, what is the product of Cyanohydrin formation?

A molecule with both an $OH$ group and a $CN$ group on the same carbon, formed using $HCN$ and $KCN$.

What is the purpose of the Wittig reaction?

To prepare alkenes from aldehydes or ketones using a phosphorus ylide.

What is the migratory aptitude for groups in the Baeyer-Villiger Oxidation?

H > 3{^\circ} > 2{^\circ}, ph > 1{^\circ} > Me

What is the physiological $pH$, and how does it affect the state of carboxylic acids?

Physiological $pH$ is $7.3$. Carboxylic acids (with $pKa \sim 4-5$) exist primarily in their carboxylate ($RCOO^-$) form.

Name the carboxylic acid derivatives in order of decreasing reactivity toward Nucleophilic Acyl Substitution.

Acid halide > Acid anhydride > Ester > Amide

What is Fischer Esterification?

The formation of an ester by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst ($H^+$).

What does the Wolff-Kishner reaction accomplish?

It reduces a carbonyl group ($C=O$) to a methylene group ($CH_2$) using hydrazine ($H_2NNH_2$) and $KOH$, heat.

In enol-enolate chemistry, what is the difference between an enol and an enolate?

An enol is a neutral 'alkene + alcohol' structure present in acidic conditions; an enolate is a resonance-stabilized anion with a negative charge present in basic conditions.

What is the product of an Aldol Condensation when heat is applied?

An $\alpha, \beta$-unsaturated aldehyde or ketone.

What are the two electrophilic positions on an $\alpha, \beta$-unsaturated carbonyl compound?

1. The carbonyl carbon (attacked by Grignard reagents); 2. The $\beta$ carbon (attacked by Michael donors or diorganocopper reagents).

What is the starting material and final product of a Malonic Ester Synthesis?

The starting material is diethyl malonate; the final product is a carboxylic acid with two additional carbons.

What is a Michael Donor?

A nucleophile (such as a deprotonated $\beta$-diketone or an enamine) that reacts at the $\beta$ carbon of an $\alpha, \beta$-unsaturated compound.

What characterizes the Stork Enamine Synthesis?

It uses an enamine as a Michael donor to create a $1,5$-dicarbonyl product after hydrolysis.