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