Systematic Organic Chemistry- Hydrocarbons Flashcards
If the overlap of a covalent bond is along the axis it is called a
End on SIGMA bond
When is a covalent bond formed
When two half filled orbitals overlap
If orbital lie perpendicular to the bond and overlap they are
Side on PI bonds
The more multiple bonds the more
PI binds are present
What bond is stronger
Sigma bonds are stronger than PI bonds
What is hybridisation
Process of mixing atomic orbitals on an atom to generate a set of new atomic orbitals called HYBRID ORBITALS
Bonding in alkanes with 3 2P orbitals and 1 2s
Form to four degenerate hybrid orbitals
Sp^3 hybrids and point to corners of tetrahedron to minimise repulsion
Later develop sigma bonds
In alkenes when 2s and 2 of the 3 2p orbitals
Form sp^2 hybrid orbitals which adopt a trigonal planar arrangement
Later forms sigma bonds and PI bonds
Why are alkenes unreactive
Due to the non polar nature of bonds
Alkanes react with halogens in sunlight make halogenoalkanes
Example of substitution- reaction in which atom or group of atoms in a molecule replaced by another group of atoms
What kind if reaction is a substitution between an alkali and halogen
Chain reaction with 3 stages
Initiation
Propagation
Termination
What is homolytic fusion in initiation
Using UV light to provide energy to break bonds and split mols into atoms
Occurs with little or no polarity in bonds
What are radicals
E ample chlorine atoms
Are atoms or groups of atoms with unpaired electrons
Extremely unstable and highly reactive
Produced by initiation step
What happen in propagation
Radicals attack other reactant mol removing hydrogen to for other radicals of different kinds
Propagating or sustaining chain reaction
Radical represented by dot
Explain the termination step
As the number of radicals build up collisions occur and stable mols are produced
Radicals used up and not produced
Chain reaction to an end
How are alkenes prepared
Dehydration of alcohols
Base induced elimination of hydrogen halides from monohalogenoalkanes
How is the dehydration of alcohols done
Alcohol vapour passed over hot aluminium oxide or alcohol treated with conc phosphoric acid
Elimination reaction
What is base induced elimination of hydrogen halide from monohalogenoalkanes
Heating monohalogenoalkanes under reflux with ethanolic potassium hydroxide (dissolved in ethanol NOT water)
Can result in formation of two alkenes
What reactions do alkenes undergo
Addition reaction to form Alkanes Halogens dihaloalksnes Hydrogen halides to form monohalogenoalkanes Water To form alcohol Add hydrogen = hydrogenation Halogen= halogenation Hydrogen halide = hydro halogenation Water = hydration catalysed by an acid
What is markovnikovs rule
States the main products of the reaction between the unsymmetrical alkene and water/hydrogen halide where hydrogen atoms add to the carbons of the double bond with larger num of hydrogen atoms already attached
The mechanism for the halogen alkene reaction is
- = bromine mol approaches double bond and becomes polarised
Electron rich double bond pushes electrons in bromine mol towards bromine atom which is remote gaining a slightly negative charge and positive charge between two bromine atoms
Cyclic ion intermediate formed song with bromide ion (electrophile = electron pair acceptor ) bond in bromide breaks said to have undergone heterocyclic fission - = the br- ion attacked he intermediate ion from opposite side acting as a nucleophile (an electron pair donor) seeking out the central positive ion
What is the process of hydrhalogenatio
- = H-br mol already polarised as H already slightly positive so it attacks the double bond forming an intermediate called carbocation
Bond in H-Br mol is breaking heterolytically and a bromide ion is formed as well - = bromide ion attacks carbocation intermediate
Attacking from either side
A halogen actsbunsymmetricalky with an alkene (two possible products)
Explain acid catalysed hydration
H ion from acid acts as an electrophile and attacks electron rich double bond to form carbocation
Then carbocation undergoes a nucleophile attack from water mol
New alcohol very strong readily looses an proton
Hydrogen released at the end
