Organic Flashcards
(22 cards)
What are hydrocarbons generally characterized by?
Generally unreactive, non-polar, and contain only single C–C bonds in alkanes
Alkanes are known as saturated hydrocarbons.
How does the volatility of alkanes change with the number of carbon atoms?
Volatility decreases and melting point/boiling point increases as the number of carbon atoms increases
This is due to increasing Van der Waals forces.
What is the general equation for hydrocarbon combustion?
C_xH_y + (x + y/4) O_2 → x CO_2 + (y/2) H_2O
This represents complete combustion.
What products are formed during complete combustion of alkanes?
Carbon dioxide and water
Complete combustion occurs when there is sufficient oxygen.
What products are formed during incomplete combustion of alkanes?
Carbon monoxide, carbon (soot), and water
Incomplete combustion occurs with limited oxygen.
What types of reactions do alkanes undergo with halogens?
Substitution reactions
An example is the chlorination of methane.
What is the first step in the chlorination of methane?
Initiation: breakdown of chlorine into radicals using UV light
This step starts the reaction.
What occurs during the propagation step of the chlorination of methane?
Chlorine radical reacts with the alkane, maintaining the balance of radicals
This involves a chain reaction.
What is the termination step in the chlorination of methane?
Chlorine radical and alkyl radical react, stopping the propagation
This reduces the number of radicals.
What is cracking in the context of hydrocarbons?
Breaking of large alkanes into smaller, more useful products using heat and a catalyst
Products can include smaller alkanes, alkenes, or hydrogen gas.
What are the two types of cracking?
- Thermal cracking: high temperature and pressure
- Catalytic cracking: high temperature and catalyst
What is the source of alkanes?
Crude oil
Fractional distillation is used to separate alkanes from crude oil.
What is the general formula for alkenes?
CnH2n
Alkenes are unsaturated hydrocarbons with at least one C=C double bond.
Why are alkenes more reactive than alkanes?
Presence of a double bond makes them more susceptible to attacks by electrophiles
Pi electrons are loosely held.
What is Markovnikov’s principle?
An electrophile adds to an unsymmetrical alkene to form the most stable carbocation
Hydrogen binds to the carbon that is more stable.
What is the reaction of hydrogenation?
Alkene + H2 → Alkane
Requires nickel catalyst, 100°C, and 2 atm pressure.
What is the condition for halogenation of alkenes?
Room temperature and in the dark
This applies to both dihaloalkane and hydrohalogen reactions.
What does KMnO4 indicate during oxidation of alkenes?
Changes from purple/pink to colorless
This indicates the formation of diols.
What is polymerization?
Repeated addition of thousands of alkene molecules to form a macromolecule
Example: Polyethene.
What are the disadvantages of polymers?
- Non-biodegradable
- Combustion produces harmful gases like SO2, CO2 and HCl
How can polymers be disposed of responsibly?
- Recycle existing plastic
- Make polymers biodegradable by adding starch units
