OCHEM Lab Final
solvolysis
splitting by solvent
alkene
A hydrocarbon with a double bond
dehydration (elimination) reaction
Alkenes may be prepared through a _________________________________________ of an alcohol (R-OH)
balanced equation of combustion reaction of ethane
C2H6 + O2 -----> 2CO2 + 3H2O
balanced equation of combustion reaction of propane
C3H8 + 5O2 -----> 3CO2 + 4H2O
balanced equation of combustion reaction of methane
CH4 + 2O2 -----> CO2 + 2H2O
200 mL
Calculate the quantity of 0.01 M aq NaOH needed to neutralize the HCl produced by complete solvolysis of the t-BuCl in 10 ml of 0.2 M t-BuCl in acetone
inert to chemical reactions
In the absence of a spark or a high-intensity light source, alkanes are
alkyl bromide
In the presence of light, or at high temperatures, alkanes react with bromine to form
alkyl halides
In the presence of light, or at high temperatures, alkanes react with halogens to form
(CH3)2CHCH2CH2CH2I
Which of the following compounds will undergo a SN2 reaction most readily?
because cyclohexene has a lower boiling point than cyclohexanol
Why does cyclohexene distill over to the receiving flask while cyclohexanol remains in the reaction flask?
The iodide of potassium iodide acts as a strong nucleophile and bromine and chlorine atoms are good leaving groups. Sodium iodide then increases the reaction.
Why does sodium or potassium iodide replace chlorine or bromine atoms in SN2 reactions? Explain your reasoning.
Bromide ion can not replace OH due to the fact that the bromide ion is a weaker nucleophile than OH. However, since OH is a good leaving group, it allows bromide ion to replace OH
Why does the reaction of bromide ion with 1-butanol require a strong acid to complete substitution?
because the bonds of ethane are partially broken in order to allow for bromine to fit in the molecule of ethane. bromine is added across the double bond.
Why is the reaction of ethane with bromine called an addition reaction?
alkane
a hydrocarbon with only single bonds
chemical kinetics
study of how the chemical changes in a predefined experimental condition affect the rate of a chosen reaction
3 degree (tertiary)
tert-butyl chloride has an electronegative chlorine atom attached to a __________ carbon
3, carbocation intermediate
the accepted mechanism of dehydration involves a ____ step sequence involving a _______________________
half-life (t 1/2)
the amount of time that it takes for the concentration of reactant to decrease to half of its initial concentration
positive, unsaturation
the disappearance of the bromine color is a ________________ reaction of __________________
faster
the more stable the carbocation intermediate, the _______________ the rate of dehydration will occur
linear equation
the rate law equation for a first order reaction is NOT a
k
first -order rate constant
cis isomer of an alkene
has the carbon groups attached on the same side of the double bond
trans isomer
has the groups attached on opposite side
decrease, time
the rate of this 1st order chemical reaction can be expressed as the __________________ in concentration of reactant per unit of ____________ (or the increase in the [HCl] per unit time)
E1 elimination reaction
the removal of an HX substituent results in the formation of a double bond.
H2O, CN-, HC---C-, CH3-, OH-
what are some examples of nucleophiles?
SN1 and SN2
what are the 2 different substitution reactions?
1. you can use the titration data to figure out exactly how much tBuCl we started and how much was present at each point along the reaction progress 2. you can calculate the volume of base needed is proportional to the amount of tBuCl
what are the 2 ways to get the rate constant?
1. the experimental condition 2. concentrations of reactants 3. the nature of the solvent 4. the process temperature
what can affect rates of chemical reaction?
the cyclohexanol molecule will lose a molecule water as the reaction proceeds. Cyclohexanol will lose the -OH group and a -H atom on the adjacent carbon to form a carbon-carbon double bond
what happened in the dehydration reaction in the experiment?
because the base deprotonates one of the phenolic OH groups
what is the reason for bromthymol blue indicator exhibiting blue?
phosphoric acid allows cyclohexanol to be protonated and which generates a stable OH2 leaving group and a carbocation. It also completes the elimination by forming the C-C double bond by removing the hydrogen of cyclohexanol.
what role does phosphoric acid play in this reaction?
7.4 ml of cyclohexanol and 1.75 mL of 85% H3PO4
what was added to the rbf of experiment 9?
combustion
when a hydrocarbon burns in presence of oxygen
purple ------> brown
when potassium permanganate reacts with an alkene what color change occurs?
t-butyl alcohol
which of the alcohols named below will react fastest with HCl to form the corresponding alkyl chloride via an SN1 pathway?
by heating the alcohol in the presence of an acid catalyst, such as phosphoric acid (H3PO4)
how is a dehydration reaction of an alkene achieved?
aromatics
hydrocarbon with a benzene ring
window light
if the bromine test is negative, shine __________________ directly on tube for 4-5 minutes
17.1 g
Please determine the correct mass in grams if you were to start with 0.15 moles of 2-methylcyclohexanol
carbocation
SN1 reactions produce a racemic mixture because the mechanism involves a intermediate
inversion of configuration
SN2 reactions involving a chiral halide/substrate usually proceed with:
proceed with nucleophilic backside attack and are stereospecific
SN2 reactions usually
As temperature increases, the molecules start to collide more frequently allowing it to overcome the activation energy. (It lowers the activation energy)
The measurement of reaction rates as a function of temperature provides information on the activation energy for the reaction. Please explain
true
The rate of a first order chemical reaction is proportional to the concentration of electrophile.
reactive
Unsaturated hydrocarbons such as alkenes and alkynes are much more ________________ than the parent alkanes
primary halide and strong Nuc-
What are the experimental factors that favor a SN2 reaction?
dark red -----> colorless (bromine and alkene) purple -----> brown (potassium permanganate and alkene)
What changes in color occur when bromine or KMnO4 reacts with an alkene?
substitution, nucleophilic, unimolecular
What does the term SN1 mean?
the product of combustion of an organic compound is carbon dioxide and 2 molecules of water. This occurs when methane gas reacts with 2 molecules of oxygen
What is the product of combustion of an organic compound? Give an example
products
What side would the equilibrium favor if we diluted (added water) to the phosphoric acid (H3PO4) before starting the reaction?
The effect of carrying out reaction 1 with concentrated iodide solution would be that it would give it a SN2 reaction.
What would be the effect of carrying out Reaction 1 with concentrated sodium iodide solution?
87%
What would the actual percent yield of the above reaction be if we started with 5.4 g of 2-methylcyclohexanol and isolated 3.9 g of 1-methylcyclohexene?
8.4 g
What would the theoretical yield (in grams) for the given reaction if you started with 10.0 g of 2-methylcyclohexanol?
addition reaction, disappears quickly
When bromine (Br2) reacts with alkene, it undergoes ________________________________ and the dark red color of Br2 _____________________________
Nucelophilic substitution
a reaction in which an incoming nucleophile replaces an existing functional group
SN1
a two step reaction, involving the formation of a carbocation intermediate, followed by a nuceophilic attack
cyclohexane was present due to the fact that the color change went from red to colorless
after dehydration reaction and transferring 10 drops of it into test tube A with 1 drop of 2% Br2, what was present and why?
carbocation, E1 elimination reaction
because the carbocation is a high-energy intermediate, the rate of dehydration depends upon the structure of the _____________________________, and therefore, is considered an _________________________________________
high temperatures
bromthymol blue indicator does NOT work properly under
positive
brown manganese dioxide (MnO2) precipitate in a potassium permanganate test indicates a __________________ reaction
larger
carbocations are more stable (lower in energy) when they have a ___________________ number of alkyl groups adjacent to them
CH3-HC--CH-CH3
condensed structure of cis-2-Butene
(CH2)4CH--CH
condensed structure of cyclohexene
CH2CH2
condensed structure of ethene
CH2CHCH3
condensed structure of propene
yellow
in acidic conditions, bromthymol blue indicator exhibits
blue
in basic conditions, bromthymol blue indicator exhibits
SN2
involves 2 different reactants and one reaction rate that determines the steps. Is a one-step reaction involving a back-side nucleophilic attack
activation energy
measurements of reaction rates as a function of temperature provides information on the ______________________________________ for the reaction
lone pairs of electrons and may carry a negative charge
nucleophiles have
positive charged centers (i.e carbocation)
nucleophiles seek
alkenes
potassium permanganate can ONLY react with
alkenes, alkanes, aromatics
potassium permanganate reacts with _______________, but not ______________ and _________________________ compounds
monitor the validity of a proposed mechanism
reaction kinetics can be used to
the decrease in concentration of reactant(s)/the increase in concentration of product(s) as a function of time
reaction rates can be determined by monitoring