Orgo Lab 8

consider the structures of 1-hexanol and cyclohexanol in the presence of heat, _____ will undergo a more effective dehydration reaction because it is a _______ alcohol and the ______ in the intermediate of the mechanism will be more stable

cyclohexanol, secondary, cation

According to the LeChatelier's principle, ____causes a shift of the reaction equilibrium towards ____ (a) Removing the product; reactant formation (b) Removing the product product formation (c) Adding more reactant ; reactant formation (d) Adding more reactant ; product formation (e) B and D

e

chemical reaction for the dehydration of 2-methylcyclohexanol and 4-methylcyclohexanol

elimination

chemical reaction of any acid with secondary alcohols

elimination

markovnikov's rule

hydrogen will add to the least substituted carbon of the double bond

lechatelier's principle

if a stress is applied to a system at equilibrium, the system will shift to reduce the stress

chemical reaction of any acid with primary alcohols

substitution

describe the role of the acid catalyst in the dehydration of an alcohol

the acid protonates the hydroxyl group and then the conjugate base deprotonates an adjacent carbon

how can a catalyst be recognized in a mechanism

the catalyst is used and then regenerated in a later step

what are the concerns presented by overheating a distillation to a dry flask

-the empty glassware might heat quickly, igniting vapors from the distillation -the remaining solid residue might contain explosive peroxides

role acid catalyst

-acid protonates hydroxy group to make a good LG of water -conjugate base removes H to from C adjacent to cation in intermediate -acid is regenerated throughout reaction -most common acids are sulfuric or phosphoric

test to determine the presence of cyclohexanol

-bromine test -bromine will readily react with alkene double bond and lose reddish-brown color -if there is cyclohexanol, bromine will not be entirely consumed and will retain some red color

E2 reaction

-concerted (LG leaves and H+ is removed in same step)

-when performing the acid catalyzed dehydration of an alcohol, the yield of product can be increased by ______ during the reaction -the dehydration is _____ and removing the product from ______ reduces the _____ reaction

-distilling off the product -reversible, the reaction flask, hydration

-the dehydration of a secondary alcohol like cyclohexanol is a mechanism that occurs in ______ -first, the alcohol is protonated to ________, creating _____ intermediate -then, a _____ is removed, moving the electrons from that bond to make a ________ bond

-in two steps -leave as a water molecule, a cation -hydrogen ion, carbon-carbon double bond

dehydration of an alcohol

-loss of water from alcohol produces alkene -alcohols do not easily undergo base-catalyzed eliminations because OH- is a poor LG -under acidic conditions, hydroxyl group can be protonated to form a better LG

E1 reaction

-occurs stepwise (LG leaves, then H+ removed by weak base) -polar protic solvent -major product is more substituted (Zaitsev) -carbocation rearrangements possible -hydride shift: H moves from one C to another adjacent C in order to reach more substituted carbocation -tend to favor trans product

if the dehydration of an alcohol is successful, what changes would be seen in the IR spectrum for the product compared to the starting material

-the disappearance of a C-O band from the starting material -the addition of a C=C band in the product -the disappearance of an O-H band from the starting material

why does the dehydration of an alcohol more often use sulfuric acid as the acid catalyst rather than dilute HCl

-the presence of the chloride ion could result in a competing substitution reaction -the additional water solvent from a dilute solution could reverse the dehydration reaction

dehydration of 1-methylcyclohexanol may result in formation of

4-methylcyclohexene

1-hexene

C6H10

2-hexene

C6H10

cyclohexene

C6H10

chemical equation for experiment

C6H11OH (cyclohexanol) --(85% H3PO4 and heat)>> C6H10 + H2O

cyclohexane

C6H12

reaction mechanism for this experiment

E1

what is the function of 9M sulfuric acid in this lab

acid catalyst for protonating the alcohol

zaitsev's rule

an elimination usually gives the most substituted alkene product.

where should the tip of the thermometer be placed in a microscale distillation set up

at or slightly below the side arm of the distillation head

what is the purpose of sodium bicarbonate in lab

it removes any excess acid

reactivity in acid catalyzed dehydration

methanol < primary < secondary < tertiary