7.2 Hydrocarbons Flashcards
How can hydrocarbons be classified based on their structure and reactivity?
haloalkanes are…
alkanes where H atoms are replaced by a halogen
naming haloalkanes
(1) place halo functional group at the front, alphabetically
(2) add “o” to the stem e.g. bromine = bromo
highest and lowest priority functional groups
highest = carboxyl group
lowest = halo group
alcohols contain what functional group
-OH
naming alcohols
ending e –> ending ol
methane –> methanol
but-1-ene –> but-1-ol
explain primary, secondary, tertiary alcohols
depends on how many other Carbon atoms the -COH has bonded with
primary amines contain what functional group
amino functional group -NH2
naming primary amines
ending e –> amine
ethane –> ethanamine
secondary and tertiary amines
N-methyl…
N,N-dimethyl…
amines produce … in dissolution
alkylammonium and hydroxide ions
amines + acid –>
alkylammonium salts + nonmetal ion
amines are weak/strong bases
WEAK, due to the lone pair of electrons on their N atoms… and somewhat polar
amides are … [acidity]
neutral
carboxyl functional group is
-CO
aldehyde vs ketone
aldehyde has carboxyl group AT THE END of the hydrocarbon chain
ketone has carboxyl group IN THE MIDDLE
naming aldehydes
ending e –> ending al or using -dehyde
propane –> propanal
naming ketones
ending e –> one
butane –> butanone
what is the simplest ketone?
propanone CH3 COCH3
aka acetone
carboxylic acids contain functional group…
-COOH
(at end of the chain)
naming carboxylic acids
ending E –> OIC acid
ethane –> ethanoic acid
primary amides contain…
carboxyl functional group connected to amino functional group
naming amides
ending E –> ending AMIDE
methane –> methanamide
what are esters
product of alcohol and carboxylic acid
naming esters
-COO- (C)
(in middle of chain)
ester equation
alcohol + carboxylic acid ⇌ ester + water
naming esters
ending E –> OATE
alcohol + carboxylic acid
ethanol + propanoic acid ⇌
ethyl propanoate (pineapple)
order of 9 priority functional groups
carboxyl
amide
carbonyl (aldehyde)
carbonyl (ketone)
hydroxyl
amine
alkene
alkyne
halo
force between, polarity, and boiling pt of alkanes
dispersion forces (weak)
non-polar
low boiling point
boiling and melting point of hydrocarbons depends on…
number of carbon atoms (chain length)
melting point for odd number carbons vs even number carbons
even number carbons pack more efficiently in solid state
= stronger dispersion forces
= requires more energy to melt
= steeper increase in melting point increment on a MP graph
alkene BP is lower/higher than alkanes
LOWER
the more branching, the __ the BP
LOWER
smaller dispersion forces for less compact hydrocarbons
order of highest BP of hydrocarbons
alkene < alkane < alkyne
why alkyne BP is highest
electrons making up bonds are more polarisable
= stronger London dispersion forces
= higher BP
hydrocarbon density >/< water
LESS than water
solute can dissolve in solvent if…
solute-solvent intermolecular forces are similar to solute-solute and solvent-solvent
what happens when you introduce halogen to hydrocarbon
larger electronegativity difference = more polar = more soluble
the longer the hydrocarbon chain =
greater dispersion forces = less soluble
what is volatility
ease which substance enters gaseous state (boiling pt)
what is flash point
minimum temp. which small flame causes the vapour above a liquid in enclosed area to ignite
the higher molecular mass, the higher BP, the … flash pt
higher
ignition temperature is…
temp. substance needs to be heated before spontaneous combustion occurs (of fuel-oxidiser mixture)
hydrocarbon fuels are stored and transported as … because…
as LIQUIDS because they occupy smaller volumes than gaseous state
- under pressure to keep liquefied
haloalkanes have higher/lower? BP than hydrocarbons because …
HIGHER BP because dipole-dipole attraction > just dispersion forces
are hydrocarbons miscible with water and why
NO because hydrocarbons are less dense than water
large difference in attraction of solute-solute and solvent-solvent intermolecular forces
when will organic-organic be miscible?
NP+NP or P+P are miscible (similar forces of attraction)
difference between haloalkanes and CFCs
haloalkanes = one or more H is replaced by halogen
chlorofluorocarbons = haloalkanes that only contain carbon, Cl, F
halons
only contains carbon, bromine + other halogens
why CFC depletes ozone layer
decomposition of CFC releases Cl atoms which catalyse ozone depletion
why HCFCs are banned
hydrochlorofluorocarbons mostly break down in atmosphere
BUT small portion decomposes in stratosphere and can still release Cl atoms
why HFCs are banned
hydrofluorocarbons = no Cl means ozone-destroying capacity is 0
BUT got banned bc it’s a strong greenhouse gas
why CFC effect on ozone layer is seasonal (Antarctica’s ozone hole)
winter is dark and cold, no heat or light energy to decompose Cl2 gas
spring sunlight splits Cl2 gas into 2 Cl atoms (destroys ozone at greater rate)
how to test for C=C double bonds
differentiate from C-C single bond
use bromine water (Br2 + water)
OR bromine dissolved in organic solvent e.g. hexane
WITHOUT THE PRESENCE OF UV LIGHT bc that’ll decolourise both alkenes and alkanes
what colour is bromine
orange-red
how to test for carboxyl functional group
carbonates, indicators, and alcohols
carbonate + carboxylic acid test reaction
NaHCO3 carbonate salt + acid –> organic salt + CO2 + water
FIZZING, effervescence via limewater test
organic acid + alcohol produces…
fruity ester
how to test for hydroxyl functional group i.e. alcohol
dry sample + metallic sodium –> product + H2(g)
slow BUBBLES
why alcohol mustn’t contain water when testing it with metallic sodium
sodium metal reacts violently with water
1st and 2nd alcohols can be oxidised by…
acidified potassium dichromate (K₂Cr₂O₇) or potassium permanganate (KMnO₄)
primary alcohol oxidises to…
aldehyde, then carboxylic acid
primary/secondary alcohol w/ K2Cr2O7 colour change on heating
orange to green
primary/secondary alcohol w/ KMnO4 colour change on heating
purple to colourless
how to test for tertiary alcohol
fast reaction with ZnCl2/HCl mixture
secondary is slow reaction
primary has no reaction
