Organic Chemistry 1 Lab Final Texas A&M Part 2

Considering the reaction of 2A + 3B goes to 1C + 3D, with molecular weights being 150, 200,
200, and 233 for A, B, C and D respectively, what would the theoretical yield for C be if you
started with an excess of B and 75 grams of A.

50g - this is a 2:3:1:3 ratio, the first step is to find the moles of A by dividing 75/150 and you get 0.5 moles, then you need to divid by 2 to make the ratio of A:C 1:1, now you have 0.25 moles and you multiply that by the molecular weight of C which is 200. 0.25 x 200 = 50g

Steam distillation is a good method for the isolation of high boiling compounds because the
vapor pressure for an immiscible mixture is equal to the _________ of the two compounds'
vapor pressures.

sum

What characteristic bond stretching does an aldehyde have in its IR spectrum that makes it easy
to differentiate it from a ketone, a carboxylic acid, or an amide?

a C-H stretch at approximately 2700 cm-1

4. A dichloromethane solution contains three compounds; A, B, and C. When this dichloromethane
solution is extracted with aqueous sodium hydroxide, one obtains a basic aqueous solution of
Compound A and a dichloromethane solution of compounds B and C. If this latter
dichloromethane solution containing B and C is extracted with aqueous hydrochloric acid, one
obtains an acidic aqueous solution containing the salt of compound B and a dichloromethane
solution containing compound C. Of the following, Compound B is most probably:
a. pentane
b. benzoic acid
c. naphthalene
d. sodium sulfate
e. benzocaine

Benzocaine

A good recrystallization solvent has the ability to________ the solute at elevated temperature

dissolve

A good recrystallization solvent has boiling points ________ the melting point of the solute

below

A good recrystallization solvent has ______ ability to dissolve the solute at low temperatures

poor

A good recrystallization solvent has _____ toxicity

low

A good recrystallization solvent has _____ volatility

high

These substances have a tendency to evaporate at normal temperatures - this is why the containers should be capped and these organic compounds should be transferred in the hood

Volatile

In the Who Has My Compound? experiment (among other experiments) you performed thin
layer chromatography on a number of compounds and used the Rf values to help determine
who else had the same compound as you had. Based on the structures of the following
molecules, which would you expect to have the lowest Rf value when run in 50/50 EtOAc and
Hexanes.

a compound containing an alkyl halide will have a low Rf value

There is a maximum quantity of sample that should be injected for preparative gas chromatography separations. This maximum quantity is determined by:

loss of resolution (separation) with increasing injection size

What change in naphthol's structure upon forming naphthyl ether will allow you to determine if the reaction is complete by IR?

loss of O-H stretch

Unimolecular nucleophilic substitution reactions: 2 steps

1. Leaving group leaves forming a positively charged carbocation (rate limiting step)

*The rate of rxn depends only on the concentration of the substrate
rate = k [R-L]
R-L is the alkyl group containing the leaving group

*Anything that accelerates the formation of the carbocation increase the rate of rxn

2. Nucleophile attacks the carbocation (unstable)
*results in substitution product

SN1

-1 step (concerted)
-Reaction rate is dependent on concentration of R-X and Nuc
-Prefers methyl, primary, or secondary carbons
-Strong nuc/strong base (OH-) or strong nuc/weak base (I-, CH3CO2-) required for methyl, primary, and secondary

SN2

a concerted elimination reaction involving a transition state where the base is abstracting a proton at the same time that the leaving group is leaving. The anti-coplanar transition state is generally preferred. Zaitsev orientation is usually preferred unless the base or the leaving group is unusually bulky.

E2

a multistep elimination where the leaving group is lost in a slow ionization then a proton is lost in a second step. Zaitsev orientation is generally preferred.

E1

How does a change in dipole moment effect IR absorption?

Bond stretching, causing a change in dipole moment, results in an IR absorption peak.

In attempting to recrystallize impure benzoic acid, it was found that the benzoic acid formed a layer of oil on top of the recrystallizing solvent as the solution cooled. How could this problem be solved?

Reheat the solution to completely dissolve the oil, add a small portion of hot solvent,
and allow the solution to cool slowly.

Mixture of two substances which result in a lower melting point than that of each individual constituent.

Eutectic Mixture

What would be the best method for the separation of 0.5g of a mixture of two liquids (bp 150 C and 160 C)

Preparative Gas Chromatography

the use of gas chromatography to separate and purify volatile organic compounds, where only small quantities of samples may be available

Preparative Gas Chromatography

What type of substitution is involved in the preparation of a naphthol ether

SN2

The phase transfer catalyst used in the experiment is a

quaternary ammonium salt

In the oxidation of cyclohexanol to cyclohexanone with bleach solution(NaOCl), the oxidation state of
what element is reduced?
a. Cr
b. hydrogen
c. Cl
d. O (of hypochlorous acid)
e. C (attached to C=O of acetic acid)

Cl

In an SN2 reaction, if the concentration of the nucleophile is doubled, the rate of the reaction will

be doubled

In an SN1 reaction, if the concentration of the nucleophile is doubled, the rate of the reaction will

not be effected

As the temperature of a liquid increases, the vapor pressure _____________

increases

If two compounds are close in boiling points, which might be a good technique to separate
them?

Gas Chromatography

_______________ can separate compounds based on polarity

Gas Chromatography

In considering rotation about the C2-C3 bond of butane, how many conformations are
encountered?

an infinite number

In IR what kind of absorption can help you identify the cyclohexene formation for certain?

presence of a peak around 1650 cm-1 and 3010-3100 cm-1

Why would an organic substance dissolve in a basic sodium bicarbonate solution which is mostly water?

The compound reacts to make a charged compound

Common TLC stationary phases include

silica gel, alumina, and microcrystalline cellulose

Phase transfer catalysts are applied to

heterogeneous organic reactions

Phase transfer catalysts can change the

solubility of the reagents

Phase transfer catalysts are soluble in

organic solvents

What product(s) can be prepared through the oxidation of primary alcohols?

aldehydes and carboxylic acids

For a first order reaction, the specific rate constant is found by

the slope of a line found by plotting ln([A]o/[A]t) versus time

In a Gas Chromatograph, the liquid adsorbed on to the column packing is usually referred to as:

the stationary phase

mixture of 2 or more substances that distills at a constant temperature and with constant composition, even though separately the components have different boiling points

azeotrope

Acetone is _______ in water, which makes it a bad solvent

soluble

What is the predicted hybridization of the oxygen in ethanol

sp3

Eugenol is a

steroid

Limonene is a

Terpene

A nonvolatile impurity dissolved in a liquid ________ the boiling point and __________ the vapor pressure

raises, lowers

What are the two main properties of compounds necessary to do a successful gas
chromatography?

Thermal stability and volatility

In a thin layer chromatography experiment, a compound is found to have an Rf close to unity(1.0). The spot for this compound on a TLC plate is most likely to appear:

slightly below the solvent front