Hydrocarbons, Alcohols, and Substitutions Flashcards
methyl, primary, secondary, tertiary, qaternary carbons on alkanes
methyl - bonded to chain with no other carbons
primary - bonded to one other carbon/bonded to the chain and one other carbon
secondary - 2…
tertiary - 3…
boiling point properties of alkanes
increase as carbons added - molecular weight and intermolecular forces increase
branching lowers boiling point
melting point properties of alkanes
increases with increasing molecular weight
branching increases melting point
density of alkanes
lowest density of all groups
density increases with molecular weight
alkane solubility
almost totally insoluble in water
soluble in benzene, carbon tetrachloride, chloroform, and other hydrocarbons
if alkane contains polar functional group, polarity and solubility of molecules decreases as carbon chain is lengthened
alkanes of four carbons or less are ___ at room temp
gases
ring strain is zero for….
cyclohexane, increases as rings become larger and smaller
the ___ conformer of cyclohexane predominates
chair - lowest energy
equatorial hydrogens
hydrogens projecting outward from the center of the ring
axial hydrogens
projecting upward or downward in ring
when ring reverses its conformation, all the hydrogens….
reverse their orientation (equatorial axial)
large substituents in axial position…
crowding occurs, raises energy level –> less stable
combustion
when alkanes are mixed with oxygen and energy is added
high temps (inside flame)
radical reaction
CH4 + 2O2 –> CO2 + 2H2O +heat
heat of combustion
change in enthalpy of a combustion reaction
the higher the heat of combustion, the higher the…
higher the energy level of the molecule, less stable
Alkanes will react with halogens in the presence of heat or light to form a ___ ___
free radical: highly reactive species with unpaired e-
halogenation
- initiation: halogen starts as diatomic molecule, homolytically cleaved by heat or light –> 2 free radicals
- propagation: halogen radical removes H from the alkane –> alkyl radical. alkyl radical reacts with diatomic halogen –> alkyl halide and new halogen radical
- termination: 2 radicals bond or a radical bonds to the wall of the container to end the chain reaction or propagation
reactivity of halogens from most reactive to least
F, Cl, Br, I
___ are more acidic than ____
alkenes are more acidic than alkanes
the more highly substituted the alkene, the more ____
the more thermodynamically stable
elimination reaction –>
alkene
dehydration of an alcohol
E1 reaction, alcohol forms an alkene in presence of hot concentrated acid
E1
rate depends upon concentration of only 1 species
carbocations
carbocation stability
most: tertirary, secondary, primary, methyl : least
Saytzeff rule
the major product of elimination will be the most substituted alkene
dehydrohalogenation
E1 (absence of strong base) or E2 (high concentration of strong bulky base)
E2 dehydroghalogenation
1 step
base removes a proton from the carbon next to the halogen containing carbon, halogen drops off leaving alkene
nucleophile
electron rich compound, donate an e pair to form covalent bond
syn addition
same side addition
in catalytic hydrogenation