Organic Chemistry & Carbon Bonding Flashcards
(24 cards)
What do the properties of organic molecules depend on?
Their structure.
Why carbon?
- can form strong bonds with many other elements and itself (high bond enthalpies)
- rare ability to catenate (long chains of carbon), allows vast range of possible structures
Give a limitation of Lewis structures.
-they do not explain the geometry of the molecules, how the bonds form, or how e- are shared between the atoms.
Define atomic orbital theory.
- region within an atom that can hold up to 2 e- with opposite spins.
- 4 types of orbital with specific shapes.
- we cannot know where an e- is at any one time, just use mathematical equations that show where the e- could possibly be.
Define px orbitals.
P orbitals that overlap head on are px orbitals that form a sigma bond, those that overlap sideways are py orbitals and form pi bonds. These combined forms a double bond.
Define a pi bond.
The pi bond is formed by the overlap of the unhybridized py orbital.
Define homologous series.
- family of chemicals with the same chemical group
- similar chemical properties
- each successive member differs by 1 carbon atom
Define alkanes.
- general formula CnH2n+2
- saturated, single bonds only.
- each carbon atom has tetrahedral geometry with bond angles of 109.5 degrees.
- non-polar.
- very unreactive: saturated, non-polar, hydrophobic. But are very good fuel sources.
Define fractional distillation of crude oil.
- complex mix of hydrocarbons.
- allows the separation of liquids depending on their boiling points.
- as chain length increase so does boiling point.
- short chains are gases, longer chains are liquid and even longer chains are solid.
Give & describe the type of isomerism exhibited by alkanes.
- exhibit structural isomerism through branching.
- structural isomers are molecules with the same molecular formula but with different structural arrangements.
Define alkanes as cyclic molecules.
- all of the C atoms in the ring are single bonded to other atoms
- still saturated hydrocarbons
- general formula CnH2n
Defines alkenes.
- general formula CnH2n
- unsaturated, double bond(s).
- more reactive than alkanes because the pi bond is weaker than a sigma bond.
- suffix = -ene
Give & define the type of isomerism exhibited by alkenes.
stereosiomerism
- free rotation around single bonds
- the double bond does not allow this
- stereoisomers are molecules with the same structural formula but with different arrangements of atoms in space.
- cis = heaviest groups are on same side of double bond
- trans = heaviest groups are across the double bond
Define alkynes.
- general formula CnH2n-2
- functional group is a triple bond (sigma + 2 pi)
- more reactive than alkenes because 2nd pi bond s even weaker than the first.
Define the effects of structural isomerism with organic halides.
- chemical behaviour is different.
- physical properties are usually different.
Define the effects of stereoisomerism with organic halides.
-physical properties are usually different.
Define the effects of optical isomerism with organic halides.
- molecules with chiral centres can exist as two optical isomers.
- mirror images of each other & are non-superimposable.
- rotate plane-polarised light in different direction (left or right).
- optical isomers are 2 molecules with the same chemical & structural formulae but different spatial arrangements of the atoms.
Define chiral centre.
carbon atom bonded to 4 different groups.
Explain why optical isomers have different biological properties & give an example.
- biological systems are very selective in term of the enantiomers they can tolerate.
- biological receptors often respond differently to different enantiomers of a compound.
- eg receptors in the nose are chiral, so enantiomers have different smells.
How do alcohols exhibit structural isomerism?
- primary alcohols have highest boiling points.
- primary alcohols are most easily oxidised. Tertiary alcohols cannot be oxidised at all.
What type of isomerism do all amino acids except glycine exhibit?
optical stereoismerism.
What is the structure of benzene?
Flat planar hexagon.
If benzene had alternating single & double bonds what would we expect?
To see different bond lengths.
All bonds are actually 1.40 A.
Why are highly conjugated molecules often coloured?
They often absorb light in the visible region.
