o chem lab practical

the most stable conformation of a cis-1,2-dimethylcyclohexane is

an axial-equatorial chair

in considering rotation about the C2-C3 bind if butane, how many conformatin are encountered?

an infinite number

which of the following statements is true

as the temperature of a liquid increases, the vapor pressure increases

upon simple distillation a mixture of CH3CH2OH and H2O distills at a constant boiling point and with a constant composition. this mixture is called a

azeotrope

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

be doubled

it is possible to separate benzocaine from a mixture of benzocaine and benzoic acid dissolved in methylene chloride because

benzocaine hydrochloride is quite soluble in water

which compound will form bubbles and dissolve in aqueous sodium bicarbonate

benzoic acid

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 the kinetic study of Sn1 solvolysis experiment, how was the disappearance of 1-phenyl-1-chloroethane monitored?

by monitoring the formation of HCl

common TLC stationary phases include all of the following expecpt:

calcium chloride

which of the following can be used to improve peak resolution in gas chromatography

change the temperature, use a smaller sample, change the flow rate

phase transfer catalysis operated by

changing the phase solubility of one of the reactants

the basis for separation by liquid-liquid extraction is

distribution of a compound between two immiscible liquids

in the natural product isolation experiment, which of the following statments is false?

eugenol and limonene are a steroid and a terpene, repsectively

which of the following reagents could be used to dustinguish the natural products, limonene and eugenol, from each other

ferric chloride

an example of sp2 hybridization on the central atom is

formaldehyde

which statement is true about IR frequency

frequency is listen in wave-numbers (cm-1) and frequency is directly proportional to energy

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

gas chromatography bc it can separate compounds based on polarity

allyl bromide and 1-chloro-1-phenylethane are both lachrymators. what does this mean?

have vapors that can irritate the eye, causing shedding of tears

which of the following mixtures will give the greatest separation by gas chromatography?

hexane/ hexanol

in the reaction of naphtholate anion and allyl bromide, the phase transfer catalyst

is. quaternary ammonium salt

at what temperature is a high-boiling, high molecular weight, water-immiscible compound distilled out during a steam distillation

just below the boiling point of water

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

there is maximum quantity of sample that shoud be injected for preparative gas chromatogrpahy separations. this maximum quantity is determined by

loss of resolution (separation) with increasing injection size

which of the following is not a criterion for the selection of a good recrystalization solvent?

low volatility

which of the following is true of molecular mechanics

molecular mechanics treats chemical bonds as mechanical springs

in the simple or fractional distillation of an ideal solution of two miscible liquids, the vapor contains

more of the more volatile component

successful purification of an impure solid is reflected in the melting range of the solid after each recrystallization. if purification is occuring, the range should become

narrow and the upper limit higher

a substance can be purified by Recrystallization when the impurity has the same solubility at high temperatures as the desired substance if

only a small amount of impurity is present

in cases where the investigational analytical GC is unable to separte two compounds

prep GC could not be performed using the same stationary phase

which of the following is an efficient method to separate a 50 µl mixture of benzene and toluene?

preparative gas chromatography

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

a nonvolatile impurity dissolved in a liquid

raises the boiling point and lowers the vapor pressure

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 coole,d, 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

select the best method of separation in order to separate the two components of a soliution of a non-volatile solid dissolved in a volatile liquid?

simple distillation

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

when a solution is cooled very rapidly in recrystallization

small crystals form that have a large surface area on which impurities will be absorbed

which of the following is a limitation of recrystallization?

some product will be lost

what is the predicted hybridization of the oxygen in ethanol?

sp3

what is the hybridization of the oxygen atom and the approximate bond angles around oxygen in methanol, CH3OH

sp3 and 109.5

when benzoin acid is mixed with inorganic sand, what happens to the melting point of the sample

stays the same

in the natural products isolation lab, eugenol was separated from a methylene chloride solution of colve oil by extraction into an aqueous solution. how was this done?

strong base (aqueous solution) was added and then eugenol formed a soluble salt

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

which of the following is the rate determining step in the Sn1 solvolysis of an alkyl halide?

R-Cl --> R+ + Cl-

preparative gas chromatography would be the best method for

the separation of 0.5g of a mixture of two liquids (bp 150 and 160)

for a first order reaction, the specific rate constant is found by which of the following techniques?

the slope of a line found in plotting ln(Ao/At) versus time

in a gas chromatograph, the liquid absorbed on to the column packing is usually referred to as

the stationary phase

for a nsolvolysis that follows an Sn1 mechanism, which of the following statements is not true

the use of a more nucleophilic solvent increases the rate of the reaction

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

a C-H stretch at approximately 2700 cm^-1

which of the following functional groups would have a peak between 1670-1830 cm-1 in an infrared spectrum

aldehyde, ketone and amide

what products can be prepared through the oxidation of primary alcohols?

aldehydes and carboxylic acids

the following criterion is not essential for suitable recrystallizing solvent

all impurities must be soluble in the hot solvent

what are the two main properties necessary to do a successful gas chromatography

thermal stability and volatility

which of the following is not true about phase transfer catalysts?

they are insoluble in water

consider a 360 rotation about the C2-C3 bond in butane. how many different values will be encountered as energy minima in this rotation

three

when collecting distillation product, the receiver is sometimes chilled with ice water. this is done

to prevent evaporative losses

which of the following statements is false about the bromine test

we can use hydrobromic acid instead of bromine

simple distillation is effective in separating compounds with

widely different boiling points

you use hypochlorous acid to oxidize a secondary alcohol. what is the oxidation state of the chlorine in hypochlorous acid, HOCl

+1

at what frequency in an IR spectrum will the aromatic C-H stretch absorb

3000-3100 cm-1

in the oxidation of cyclohexanol to cyclohexanone with bleach solution, the oxidation state of what element is reduced?

Cl

in the kinetic study of Sn1 nsolvolysis, the nucleophile in the reaction is

H2O

which technique would be best for the purification of a mixture which contained a large amount of a solid material with a small amount of lquid contamination? both the liquid and solid are soluble in organic solvent

Recrystallization

which of the following statements about TLC is true?

Rf values are independent of the distance the solvent travels

which of the following regents is not an oxidizing agent

SOCl2

during the dehydration of cyclohexanol experiment, you used the distillation technique to purify your product from the reaction mixture and obtained a distillate boiling at 71˚C. the distillate is an azeotrope of 90% product and 10% water. what was the most certain about the boiling point of your product

the boiling point of the product should always be above 71˚C

which of the following statements best describes a eutetuc mixture

the composition of mixtures of two elements that makes a lowest possible melting point

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

the compound reacts to make a charged compound

during the extraction lab you extracted benzocaine out of CH2Cl2. what was the reactive functional group and what reagent was used to make this happen?

the functional group was an amine and the reagent was an acid

in gas chromatography, the degree of separation of two components does not depend upon

the inert gas chosen as the mobile phase

when you tested mixture melting point temperatures in the lab, your records showed that

the melting point of your unknown compound will be lower and the range broader if you mixed it with an organic compound different from your unknown and organic compounds and insoluble inorganic compounds that do not mix when melted give a melting range that is sharp even though there are inorganic impurities in the sample.

you have 1g of a eutectic mixture of compound A and compound B. you add 0.2g of B. which of the following statements is true?

the melting range will be at a higher temperature and broader

in the phase transfer catalysis experiment, why was it possible ti purify the product through column chromatopgraphy

the product had a much larger Rf than the other components of the reaction mixture

which statement is false for the phase transfer catalysis experiment

the role of the phase transfer catalyst, benzyltri-n-butyl ammonium chloride is to carry the naphtholate anion into the water

which of the following is not a requirement for preparative gas chromatography

the sample size must be less than 5µl