Alkenes Flashcards
what is an alkene?
an unsaturated hydrocarbon that contains at least 1 carbon-carbon double bond in their molecular structure.
what is the general formula of an alkene?
CnH2n
what 2 types of bonds do alkenes consist of?
Sigma (σ) Bond: The sigma bond forms when two atomic orbitals overlap head-on. In the case of the carbon-carbon sigma bond in alkenes, the hybridized sp2 orbitals overlap end-to-end along the internuclear axis, resulting in a strong and stable bond.
Pi (π) Bond: The pi bond forms when two unhybridized p orbitals overlap side-by-side, with their electron density concentrated above and below the internuclear axis. In alkenes, the pi bond arises from the overlap of the unhybridized p orbitals of the carbon atoms adjacent to the sigma-bonded carbons. The pi bond provides additional stability to the molecule but is weaker than the sigma bond.
how do these 2 covalent bonds affect the reactivity of alkenes?
alkenes are more reactive than alkanes as the Pi bond is significantly weak and susceptible to attack by electrophiles. these attack lead to various addition reactions.
how do these 2 covalent bonds affect the physical properties of alkenes?
boiling point is lower than alkanes as the double bond introduces higher polarity within the molecule which generally allows bonds to be broken faster and lowers the boiling points of molecules.
how does a double bond affect the isomerism of a molecule?
alkenes exhibit geometric isomerism due to restricted rotation around the carbon-carbon double bond. this leads to the existence of cis-trans isomers where different spatial arrangements of substituent groups are possible around the double bond. these geometric isomers can have different physical and chemical properties, such as boiling points, melting points, and reactivity, depending on their spatial arrangement.
what are primary alkenes and what do you know about their stability?
primary alkenes where the carbon atom directly bonded to the double-bonded carbon (the carbon-carbon double bond) is also bonded to only one other carbon atom. In other words, in a primary alkene, the carbon-carbon double bond is located at the end of the carbon chain, primary alkenes are generally less stable than secondary or tertiary alkenes due to the absence of additional alkyl groups.
what are secondary alkenes and what do you know about their stability?
secondary alkenes are organic compounds that contain a carbon-carbon double bond (C=C) where the doubly bonded carbons are each bonded to two other carbon atoms. this arrangement leads to a structure where the carbon-carbon double bond is located between two alkyl groups. in other words, one of the carbon atoms of the double bond is bonded to two other carbon atoms, while the other carbon atom of the double bond is also bonded to two other carbon atoms. these alkenes exhibit moderate stability.
what are tertiary alkenes and what do you know about their stability?
tertiary alkenes have the carbon-carbon double bond located between two secondary carbon atoms, meaning that both carbon atoms directly bonded to the double-bonded carbons have two carbon atoms attached.
tertiary alkenes are the most stable among primary, secondary, and tertiary alkenes due to the higher degree of substitution around the double bond.
state the reagent, conditions, catalyst, product and equation for DIRECT HYDRATION
reagent- steam
conditions- high pressure
catalyst- phosphoric acid
product- alcohol
equation- C2H4(g) + H2O(g) ↔️ C2H5OH(g)
state the reagent, conditions, product and equation for HYDROGENATION
reagent- hydrogen
conditions- nickel catalyst
product- alkanes
equation- C2H4(g) + H2(g) → C2H6(g)
what is addition polymerisation?
an alkene undergoes an addition reaction with itself. all atoms in the original are used to form polymers.
what is PVC?
a rigid polymer, used to form pipes. joined by intermolecular bonds, permanent dipole-dipole and london dispersion forces. intermolecular forces allow chains to move over eachother.
what is deducing repeat units?
a repeat unit is the smallest group of atoms that when connected one after the other make up the polymer chain.
it is represented by square brackets in the displayed and general formula
how do you name polymers in terms of alkenes?
poly(x), where x is the alkene.
