Chapter 6: ROH Flashcards
functional group definition
structural unit responsible for characteristics, physical and chemical properties under conditions
what are the 2 different naming conventions in IUPAC
functional class substitutive
what IUPAC naming class is preffered
substitutive
main difference between functional class and substitutive names
functional - alkyl followed by "alcohol" substitutive - start with longest C chain that has the OH group number closest to OH replace -ane with -ol substituents and location BFORE parent
where is OH assumed to be attached in cyclic alcohols
C-1
does alcohol or a halogen have higher priority
OH has higher priority than halo
how is the C-O bond made in alcohols
- overlap of sp3 orbital on carbon
- overlaps with one sp3 on oxygen
- oxygen is left with 2 nonbonding e- pairs
how are bonds made in alkyl halides
-halogen is connected to the carbon with a SIGMA bond
carbon-halogen bond distances trend
C-F < C-Cl < C-Br < C-I
more electronegetive halogen = smaller bond distance
what type of bonds do alkyl halides and alcohols have
polar bonds, and may be polar molecules
dipole-dipole attractive forces
molecules with permanent dipoles have a stronger dipole-dipole intermolecular interaction than alkanes
why does flouroethane, for example, have a higher boiling point than propane
because its dipole-dipole forces are stronger (flourine is very electronegative) and therefore boiling point is higher
what is different about ethanol and its boiling point
ethanols boiling point is so high that dipole-dipole interactions are not enough to explain it
explain bonding in alcohols
alcohols have hydrogen bonding (dipole-dipole)
partially positive proton of one -OH group interacts with the partially negative oxygen of a second ethanol
hydrogen bond acceptor and donor in alcohol bonding
oxygen = hydrogen bond acceptor
OH hydrogen = hydrogen bond donor
what are the onlu elements involved in hydrogen bonding in organic compounds
oxygen
nitrogen
NO
what are alcohols and their hydrogen bonds strong enough to do
impose structural order
methyl
CH3
ethyl
CH3CH2
propyl
CH3CH2CH2
pentyl
CH3(CH2)3CH2
hexyl
CH3(CH2)4CH2
iodine and polarization
iodine is highly polarizable
why is iodine highly polarizable
because the valence electrons are far from the nucleus
induced dipole-induced dipole forces
connection between halogens, dipoles and boiling point
- increase the number of halogens (Cl, Br, I)
- increases the dipoles
- increases boiling point
flourine and polarization
flourine has very low polarizability, and boiling points do not increase as you increase the amount of flourine
solubility of alkyl halides
insoluble in water
solubility of alcohols in water
is directly related to the size of the alkyl group that the OH is attached to (the more, the less soluble)
alcohols that are totally miscible in water
methyl, ethyl, n-propyl, and isopropyl
what is the only amount of octanol that dissolves in water
1 mL 1-octonol in 2000 mL water
densities compared to water
less dense than h2O = alkyl flourides and chlorides
more dense than water = alkyl bromides and iodides, CH2Cl2
halogenation and density
increasing halogenation increases density
what are the 3 main steps in radical mechanisms
- chain initiation
- chain propagation
- chain termination
what type of arrow do you use in radical mechanisms
fish-hook arrows
what are the problems associated with halogenation of alkanes
- different hydrogens can lead to different products
2. can get over-halogenation
radical stability
methyl < primary < secondary < tertiary
synthesis
methods of preparation of alkyl halides
mechanism
the step-by-step description of how reactions take place
alcohol reaction rate
tertiary alcohols react fastest at low temps
primary alcohols react slowest and need the highest temps
bimolecular reaction
both reactants change
how is the central carbon hybridized in carbocation
sp2
positive charge is in the empty p-orbital
characteristic of carbocations
they are electrophilic
meaning they seek electrons and love them
mean they are lewis acids
SN1 nucleophile
is a nonbonding electron pair in a p-orbital that interacts with the empty p-orbital of the carbonation to form a sigma bond
in Sn1, what must the sum of each individual step equal
the overall reaction equation
what type of reaction is Sn1 and why
substituation reaction
nucleophile chloride takes the place of OH
what is important about the slow step in Sn1 step 2
unimolecular
rate determining step
the overall reaction cannot go faster than this step
where are the alkyl groups attached to stabilize a carbocation
directly attached to the positively charges carbon
how are carbocations defined
methyl, primary, secondary, tertiary depending on how many carbons are directly attached to the cationic carbon
stability vs. carbocation type
more stable as it is attached to more carbons
least stable is methyl, most is tertiary
inductive effect
alkyl groups push electron density onto C+
how is the methyl cation in inductive effect
has an intense positive charge
the more the charge is delocalized on a cation…
the more stable the cation
how are carbocations stabilized
by delocalization of electrons from the sigma bonds, to the + carbon in the empty p orbital
what does MO theory predict about bonding orbitals
predicts a bonding orbital with 2 electrons that spans the sigma bond and the positive carbon
relationship between formation of carbocation and stability
the rate of formation of the carbocation is related to the stability of the carbocation formed
what tracks the stability of the carbocation and why
the transition state is closer in energy to the carbocation
so the activation energy tracks the stability of the carbocation
what type of reaction is Sn2?
a substitution reaction
what is an alkeal
a protonated alcohol
why do primary methyls need SN2
because primary methyl carbocations are very unstable, must react in a different way
what is thionyl chloride used for in reactions with alcohol
to transform primary and secondary alcohols into alkyl chlorides (not tertiary)
what is pyridine used for
it is a base used to neutralize the acid (HCl) formed
phosphorus tribromide reacts with what to form what
reacts with alcohols to form alkyl bromides
SN2
halogenation of F2
is explosive
halogenation of I2
is endothermic
halogenation of alkanes and what they are useful for
the reaction is exothermic
useful for Cl2 and Br2
what are the intermediates in chlorination of methane
free radicals
what do free radicals contain
unpaired electrons
how do yyou classify radicals
by how many carbons they are directly attached to
primary, secondary, tertiary and methyl
hybridization of carbon atom with unpaired electron
where is the unpaired electron
sp2
unpaired electron is in the 2p orbital
what makes free radicals more stable and why
the more alkyl groups connected to the radical, the substituated and the more stable!
trend in stability for free radicals
methyl
how are radicals produced
bond cleavage
how many bonding electrons does each atom have in homolytic bond cleavage
each atom retains one of the bonding electrons
what is bond dissociation enthalpy
the energy required for bond to dissociate
what happens to bonding electrons in heterolytic cleavage
the more electronegative element retains both bonding electrons
how can we quantify radical stability
comparing the energy required for homolytic bond cleavage
relationship between stability of radicals and their bond dissociation enthalpies
the less energy, the more stable the radical
how are mono halogenation reactions of higher alkanes initiated in lab
you use light (hv)
what does cyclobutane yield in monohalogenation of higher alkanes and why
a single monochlorination product because the 8 hydrogens result in the same product being formed
relationship between transition state and abstraction of a secondary hydrogen (compared to primary)
the transition state is lower in energy for abstraction of a secondary carbon because a secondary radical is more stable
what type of hydrogen does bromination favor
tertiary substitution
what type of energy pattern is hydrogen atom abstraction for chlorination
exothermic
what type of energy pattern is hydrogen atom abstraction for bromination
endothermic
is hydrogen atom abstraction for chlorination or bromination more selective and why
bromination because it is endothermic
definition of hydrogen abstraction
removal of an atom or group from a molecule by a RADICAL
