orgo exam 2

how to find relative moles ratio

integration/# of H for both molecules

relative mass

(relative moles) x (molar mass) for each molecule

mass purity % for a specific molecule

specific molecule relative mass / total mass x 100

actual mass of isolated product

grams of molecule x mass purity in decimal

how to find yield

find the limiting reagent, use the balanced equation to find theoretical moles of product, convert theoretical moles to grams and then calculate percent yield

how to find limiting reagent

convert everything to moles

how to convert to moles

from mass: mol = g/ g/mol

mass = volume x density

how to convert theoretical moles to grams

theoretical yield = mol product x mw

how to calculate percent yield

actual yield/theoretical x 100

how to find when it asks the starting material to isolate an amount of product

find theoretical product, convert grams to moles using original ms, find and use mole ratio, convert to grams using new mw,

how to find theoretical product

desired actual product/decimal yield

what mechanism best explains dehydration of 2-methylcyclohexanol

mainly e1. acid protonates OH so water leaves, a carbocation forms, B-H is removed, and an alkene forms

what are the major possible alkene products of 2-methylcyclohexanol

1 methyl cyclohexene and 3methyl cyclohexene. the first one is favored bc is is the more substituted, more stable alkene

What happens if phosphoric acid is not added?

Dehydration is very slow or does not occur because OH is a poor leaving group unless protornated.

why use fractional distillation with a vigreux column instead of simple distillation

it gives better separation of compounds with relatively close boiling points

if pure trans 2 methylcyclohexanol were used instead of an isomer mixture, would e1 products change dramatically

not much. the planar carbocation intermediate loses the starting sterochemistry, so similar alkene products can form

why isnt 2 methylcyclohexene listed as a separate product

it is the same constitutional structure as 1 methylcyclohexene after renumbering the ring

can IR easily distinguish the isomeric alkene products

no. they have the same major funtional group, c=c, so their ir spectra are very similar. nmr is better

how can cnmr help identify an alkene product

look for sp2 alkene carbons around 100-150 ppm and compare the number and positions of carbon signals

in Hnmr, how do you know dehydration occured

the C-H attached to the alcohol carbon disappears, and alkene H signals around 4.5 to 6.5 ppm may appear

1-Bromo-1-methylcyclohexane: SN1 or SN2?

sn1 bc it is tertiary and forms a relatively stable tert carbocation. sn2 is sterically hindered

1-Bromopropane: SN1 or SN2?

sn2, bc it is primary and has little steric hindrance. a primary carbocation would be unstable

2-Bromohexane: SN1 or SN2?

since its secondary, both can occur depending on the conditions. sn2 if strong nuclephile/aprotic solvent or sn1 for polar protic/ weak nucleophile

why can benzyl bromide react readily under both sn1 and sn2 conditions

for sn1, the carbocation is esonance stabilized. for sn2, the benzylic carbon is accessible and reacts rapidly by backside attack

Why is bromobenzene unreactive under normal SN1 and SN2 conditions?

SN1 would require an unstable phenyl carbocation, while SN2 backside attack at an sp² carbon is unfavorable.

Why does bromocyclohexane react faster than chlorocyclohexane in SN2?

Br⁻ is a better leaving group than Cl⁻, and the C–Br bond is weaker.

Why does tert-butyl iodide react faster than tert-butyl bromide by SN1?

I⁻ is a better leaving group, so ionization to form the carbocation occurs faster.

Why are AgNO₃ and a polar protic solvent used to promote SN1?

The polar protic solvent stabilizes ions, while Ag⁺ helps remove the halide as AgX precipitate, promoting carbocation formation.

What controls SN1 reaction rate?

Mainly substrate concentration and carbocation stability. Rate = k[substrate].

What controls SN2 reaction rate?

Both substrate and nucleophile concentration. Rate = k[substrate][nucleophile].

Quick substrate ranking for SN2?

Methyl > 1° > 2° >> 3° because steric hindrance slows backside attack.

Quick substrate ranking for SN1?

Generally 3° > 2° >> 1°/methyl, because more substituted carbocations are more stable. Benzylic and allylic substrates are especially favorable due to resonance.

What type of reaction is nitration of methyl benzoate?

Electrophilic aromatic substitution (EAS).

What is the major product of nitration of methyl benzoate

methyl 3 nitrobenzoate, the meta product

Why does nitration occur mainly meta to –CO₂CH₃?

The ester group is electron-withdrawing and meta-directing. Ortho/para attack gives especially unstable resonance intermediates.

What is the electrophile in nitration?

The nitronium ion, NO₂⁺.

How is NO₂⁺ formed?

Concentrated H₂SO₄ protonates HNO₃, which loses water to generate NO₂⁺.

What are possible unwanted products that lower yield?

rtho/para isomers and over-nitrated products, such as dinitrated material.

What procedural mistake can increase dinitration?

Excess nitrating reagent, excessive heating, or allowing the reaction to become too vigorous.

Why use cold methanol to wash the crystals?

It removes soluble impurities while minimizing dissolution and loss of the desired product.

Why use the minimum amount of hot methanol during recrystallization?

too much solvent keeps more product dissolved after cooling, causing lower recovery/yield.

Why can methyl benzoate dissolve in concentrated H₂SO₄ even though it is water-insoluble?

The ester oxygen can be protonated, producing a more polar/ionic species that interacts strongly with the acidic medium.

What removes H from the arenium-ion intermediate to restore aromaticity?

A base present in the mixture, commonly HSO₄⁻, removes H⁺ and restores the aromatic ring.

What NMR change confirms nitration?

The aromatic pattern changes because one aromatic H is replaced by NO₂. Methyl benzoate has 5 aromatic H, while methyl 3-nitrobenzoate has 4 aromatic H.

What important IR peaks indicate the nitrated ester product?

A strong ester C=O around ~1700–1730 cm⁻¹ plus strong NO₂ absorptions near ~1500–1550 and ~1300–1370 cm⁻¹.