Chapter 10 Flashcards
Alcohol
A hydroxyl group bonded to an sp^3 hybridized carbon
How are alcohols classified?
As primary secondary or tertiary, depending on whether the hydroxyl group is bonded to a primary, secondary, or tertiary carbon.
How are IUPAC names of alcohols derived?
By changing the suffix of the parent chain from -e to -ol
How are the carbon chains of alcohols numbered?
From the direction that gives the carbon bearing the hydroxyl group the lower number.
How are compounds containing other functional groups that take higher precedence named?
The presence of the hydroxyl group is indicated by the prefix hydroxy-
How is the oxygen atom of an alcohol hybridized?
sp^3 (remember the unshared electron pairs)
___ sp^3 hybrid orbitals of oxygen form __ bonds to atoms of carbon and hydrogen, and the remaining ___ sp^3 hybrid orbitals each contain an unshared pair of electrons
Two, sigma, two
What is the parent alkane for an alcohol?
The longest chain of carbon atoms containing the -OH group.
To show the compound is an alcohol:
change the suffix-e to -ol and use a number to show the location of the -OH group
The location of the -OH group takes precedence over __________ in numbering the parent chain.
alkyl groups and halogen atoms
For cyclic alcohols, numbering begins with the carbon:
containing the -OH group
Should the number location of the -OH group be stated in cyclic alcohols?
No
In complex alcohols, the number for the hydroxyl group is often:
placed between the infix and the suffix
Diol
A compound containing two hydroxyl groups
Triol
A compound containing three hydroxyl groups
In IUPAC names for diols, triols, and so on, the ___ of the parent alkane name is retained.
final -e
Glycols
Compounds containing hydroxyl groups on adjacent carbons
Unsaturated alcohols
Compounds containing -OH and C=C groups
Alcohols are ______ compounds with oxygen bearing a partial _______ charge and both the carbon and the hydroxyl hydrogen bearing partial ______ charges.
polar, negative, positive
Hydrogen bonds
Relatively strong attractive interactions between a hydrogen atom bonded to an atom of high electronegativity, usually O or N, and a lone pair of electrons on a highly electronegative element, again, usually O or N.
The boiling points of alcohols are _____ than those of hydrocarbons of comparable molecular weight. Why?
higher
Because of the intermolecular association of hydrogen bonding
The boiling points of alcohols ______ with increasing molecular weight. Why?
increase
Because of increased dispersion forces
Alcohols are ____ soluble in water than hydrocarbons of comparable molecular weight. Why?
more
Alcohols interact with water by hydrogen bonding
What intermolecular forces do alcohols contain?
LDF, dipole-dipole, and hydrogen bonding
Hydrogen bonding is ______ than covalent bonding.
weaker
Alcohols can function as both ____ acids (proton _____) and _____ bases. (proton ______)
weak, donors, weak, acceptors
The pKa of most alcohols is:
in the range of 16-18
Loss of a proton from an alcohol produces:
An alkoxide anion, a relatively strong base
In the presence of a strong acid, the -OH group can be _______.
protonated
Protonation of the -OH group produces:
The good leaving group -OH2+ (a common mechanistic scheme for alcohols)
In dilute aqueous solution, methanol and ethanol are comparable in acidity to _____.
water
Secondary and tertiary alcohols are somewhat ______ acids than primary alcohols and water.
weaker
In dilute aqueous solution, only ______ is more acidic than water.
methanol
_______ molecular weight, _______ alcohols are slightly weaker acids than water.
higher, water-soluble
For simple alcohols such as methanol and ethanol, acidity depends on:
the degree of solvation and stabilization of the alkoxide ion by water molecules
In the presence of strong acids that generate hydronium, the oxygen atom of an alcohol is a(n) _____ and reacts with a(n) ____ by proton transfer to form a(n) _______.
base, acid, oxonium ion
Alcohols react with active metals such as ________ to:
Li, Na, K
liberate H2 and form metal alkoxides
Metal alkoxides are nearly ____ or somewhat _____ bases than alkali metal hydroxides, such as NaOH and KOH
the same, stronger
What kind of reaction is the reaction of alcohols with active metals?
An oxidation/reduction reaction
In the reaction of alcohols with active metals, the active metal (Met) is _______ to ____ and H+ is ______ to _____.
oxidized, Met+, reduced, H2
To name a metal alkoxide:
Name the cation first, followed by the name fo the anion. The name of the anion is derived from the number of carbon atoms and their arrangement followed by -oxide.
Alcohols can be converted to salts by reaction with bases _____ than alkoxide ions.
stronger
What is an example of a base that converts alcohols to salts?
NaH
Hydride is the conjugate base of H2, making it extremely strong
Reactions of sodium hydride with compounds containing acidic hydrogens are ______ and driven to completion by:
irreversible
the formation of H2, which is give off as a gas
A common theme for reactions of alcohols is the conversion of:
the -OH group into a better leaving group by protonation and/or replacement with a halogen or other group.
Alcohols can be converted to haloalkanes by reaction with:
HCl, HBr, HI, PBr3, SOCL2, or SOBr2
The HX reactions work best for tertiary alcohols when:
they involve a carbocation intermediate
PBR3, SOCL2, or SOBr2 react well with:
secondary and primary alcohols
PBR3, SOCl2, and SOBr3 reactions with secondary and primary alcohols involve ___ displacement, so:
SN2
inversion of stereochemistry is seen when they OH group is bonded to a chiral center
Alcohols react with ______ to give alkyl sulfonates.
sulfonyl chlorides
The sulfonate group is a _____ leaving group analogous to _________, so alkyl sulfonates can take part in __________.
good, a halogen atom, substitution and elimination reactions
_______ alcohols react rapidly with HCl, HBr, and HI.
Tertiary
Mixing a low-molecular-weight, water-soluble tertiary alcohol with concentrated HCl for a few minutes at room temp. results in:
conversion of the alcohol to a chloroalkane
Low-molecular-weight, water soluble _____ and _____ alcohols are unreactive when mixed with HCl for a few minutes at room temp.
primary, secondary
Water-insoluble tertiary alcohols are converted to tertiary halides by:
bubbling gaseous HX through a solution of the alcohol dissolved in diethyl ether or THF
Water-insoluble react very _____ when gaseous HX is bubbled through a solution of the alcohol in diethyl ether or THF.
slowly
Many secondary alcohols give at least some _______ product when reacted with HX, showing evidence of __________.
rearrangement, carbocation intermediates
Primary alcohols with extensive beta-branching give large amounts of ______________ when reacted with HX.
a product derived form rearrangement
What is the relative ease of reaction of alcohols with HX?
Tertiary > secondary > primary
Based on __________ and ________, chemist propose an SN1 mechanism for the conversion of ________ and _______ to haloalkanes by concentrated HX, with the formation of __________.
the relative ease of reaction,
the occurrence of rearrangements,
tertiary and secondary,
a carbocation intermediate
What are the steps of the mechanism for the reaction of a tertiary alcohol with HBr?
1) add a proton
2) break a bond to give stable molecules or ions
3) make a new bond between a nucleophile and an electrophile
Describe step one of the mechanism for the reaction of a tertiary alcohol with HBr: add a proton
Rapid and reversible proton transfer from H3O+ to the -OH group of the alcohol gives an oxonium ion, which converts -OH, a poor leaving group, into -OH2+, a better leaving group
Describe step 2 of the reaction of a tertiary alcohol with HBr: break a bond to give stable molecules or ions
Loss of water gives a tertiary carbocation intermediate
Describe step 3 of the reaction of a tertiary alcohol with HBr: make a new bond between a nucleophile and an electrophile
Reaction of the tertiary carbocation (an electrophile) with bromide ion (a nucleophile) gives the haloalkane
Primary alcohols with no beta-branching react with HX by:
an SN2 mechanism
What is the rate determining step of the reaction of a primary alcohol with no beta-branching with HX?
When the halide ion reacts at the carbon bearing the oxonium ion to displace H2O and for the C-X bond
What are the steps for the mechanism of the reaction of a primary alcohol with HBr (SN2)?
1) add a proton
2) make a new bond between a nucleophile and an electrophile and simultaneously break a bond to give stable molecules or ions
Describe step one of the reaction of a primary alcohol with HBr (SN2): add a proton
Rapid and reversible proton transfer gives an oxonium ion, which transforms -OH, a poor leaving group, into -OH2+, a better leaving group
Describe step two of the reaction of a primary alcohol with HBr (SN2): make a new bond between a nucleophile and an electrophile and simultaneously break a bond to give stable molecules or ions
Nucleophilic displacement of H2O by Br- gives the bromoalkane
Primary alcohols with extensive beta-branching react by a mechanism involving:
What is this reaction classified as and why?
formation of a tertiary carbocation intermediate by simultaneous loss of H2O and migration of an alkyl group
Classified as SN1, because the rate-determining step of the transformation involves only one reactant.
What are the steps of the mechanism for rearrangement upon treatment of a CH3C(CH3)2CH3OH (neopentyl, a primary alcohol with extensive beta-branching) with HCl?
1) add a proton
2) 1,2 shift and simultaneously break a bond to give stable molecules or ions
3) make a new bond between a nucleophile and an electrophile
Describe step 1 for rearrangement upon treatment of a CH3C(CH3)2CH3OH (neopentyl, a primary alcohol with extensive beta-branching) with HCl: add a proton
Rapid and reversible proton transfer gives an oxonium ion
Describe step 2 for rearrangement upon treatment of a CH3C(CH3)2CH3OH (neopentyl, a primary alcohol with extensive beta-branching) with HCl: 1,2 shift and simultaneously break a bond to give stable molecules or ions
Two changes take place simultaneously in this step; the C-O bond breaks, and a methyl group with its pair of bonding electrons migrates o the site occupied by the departing H2O group. The result is the loss of H2O and the formation of a tertiary carbocation
Describe step 3 for rearrangement upon treatment of a CH3C(CH3)2CH3OH (neopentyl, a primary alcohol with extensive beta-branching) with HCl: make a new bond between a nucleophile and an electrophile
Reaction of the tertiary carbocation (an electrophile) with chloride ion (a nucleophile) gives the tertiary haloalkane
Alcohols react with PBr3 to:
initially displace Br- to give a protonated dibromophosphite intermediate, which is displaced from the backside by Br- to give the bromoalkane
Although rearrangement sometimes occurs with PBr3, the extent is considerably less than:
that with HBr
What are the steps of the mechanism for the reaction of a primary alcohol with PBr3?
Step one and two are the same idea:
make a new bond between a nucleophile and an electrophile and simultaneously break a bond to give stable molecules or ions
Describe step one for the reaction of a primary alcohol with PBr3:
Nucleophilic displacement on phosphorous by the oxygen atom of the alcohol gives a protonated dibromophsophite group, which converts -OH to a good leaving group (OHPB2+, rather than OH2+)
