Organic chemistry and nomenclature Flashcards
Intro, molecular orbital theory, homologous series, alkanes, isomerism, alkenes, alkynes.
What is organic chemistry?
Chemistry of compounds containing carbon.
Carbon can bind strongly to other elements and with itself form strong…
bonds.
The combination of properties of carbon allows it to form a vast range of possible structures.
Carbon possesses the rare tendency to catenate.
What does catenate mean?
Form chains of carbon atoms.
Knowing about carbon’s electronic properties allows an understanding of the formation of…
organic molecules.
Give the relative atomic mass, atomic number and electron configuration of carbon.
Atomic mass = 12.011g/mol
Atomic number = 6
Electron configuration = 1s2 2s2 2p2
How many extra electrons does carbon require to fill the octet rule?
4
In covalent bonding each carbon atom only ever forms…
4 bonds.
What are Lewis structures?
Dot and cross diagrams = simplest and most limited theory on electronic structure.
What is atomic orbital theory?
Explains how bonds form, how electrons are shared between atoms and the geometry of molecules.
Atomic orbitals combine to form…
molecular orbitals.
A pair of electrons that form a single sigma bond occupy sigma molecular orbitals.
What is a single sigma bond?
What is a sigma molecular orbital?
Sigma bond = a covalent bond formed by the overlap of atomic orbitals.
Sigma molecular orbital = shared electron density in between bonded atoms.
Why are single covalent bonds also called sigma bonds?
Because the head on overlap of atomic orbitals form molecular sigma orbitals.
For example, the 4 covalent bonds in methane are made by the overlap of atomic orbitals on…
the C and H atoms.
What is a homologous series?
A family of chemicals containing the same functional group that have similar chemical properties and each successive member differs by one carbon atom.
What are alkanes?
Saturated aliphatic hydrocarbons with the general formula CnH2n+2.
What does hydrocarbon mean?
Compounds contain only hydrogen and carbon.
What does aliphatic mean?
Organic compounds in which carbon atoms form open chains.
What is the geometry and bond angle for each carbon in an alkane?
Tetrahedral and 109.5 degrees.
Why are alkanes non-polar?
C and H have similar electronegativities.
Alkanes are hydro…
phobic.
What are the intermolecular interactions in alkanes?
Dispersion forces = Van der waals
What is the fractional distillation of crude oil?
Separating a mixture of hydrocarbons (mainly alkanes) depending on their boiling points.
Explain why as the chain length of an alkane increases, the boiling point also increases.
As chain length increases, there are more points of contact between molecules, therefore more van der waals forces.
Give the alkyl prefixes for the first 10 alkanes.
methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl.
Then for 12 and 16 carbon atoms.
dodecyl, hexadecyl.
List 4 different ways to display molecules.
Molecular, structural, displayed and skeletal formula.
Alkanes are constantly rotating and moving in solution.
So how are they named?
- Determine the number of carbons in the
longest chain. - Number the chain so the side chain
(substituent) gets the lowest possible
number. - Deduce the number of C atoms in
(substituent) side chain. - Combine.
What are structural isomers?
e.g. heptane has 9 structural isomers.
Molecules with the same molecular formula but different structural arrangements.
What are cycloalkanes?
Cyclic saturated hydrocarbons with the general formula CnH2n+2.
Carbons of the molecules are arranged in the form of a ring. All carbon atoms in the ring are single bonded to other carbon atoms.
What are alkenes?
Unsaturated hydrocarbons with the general formula CnH2n.
Functional group = (one or more) carbon to carbon double bonds.
What geometry and bond angle do carbons involved in the double bond have?
A trigonal planar geometry with bond angles of 120 degrees.
How are molecular pi orbitals formed?
By the side on overlap of atomic orbitals.
What bonds does a carbon to carbon double bond consist of?
A sigma bond (head on overlap of atomic orbitals) and a pi bond (side on overlap of atomic orbitals)
2 electrons occupy sigma orbitals and 2 occupy pi orbitals.
Why are alkenes more reactive than their equivalent alkanes?
The pi bond is weaker than a single sigma bond.
Why is ethene specifically important in everyday life?
Ethene is a plant hormone used commercially for the ripening of fruit.
The shape of ethene is vital for this function as ethane doesn’t fit the receptor so doesn’t ripen fruit.
In alkanes, there is free rotation about the…
carbon to carbon single bond.
In alkenes, there is no rotation about the…
carbon to carbon double bond.
What isomerism do alkenes exhibit, why?
Stereoisomerism (geometric isomerism)- restricted rotation about carbon to carbon double bond means a fixed planar structure.
What are stereoisomers?
Molecules with the same molecular and structural formula but a different arrangement of atoms in space.
What is a cis/Z isomer?
Substituents are on the same side of the carbon to carbon double bond.
What is a trans/E isomer?
Substituents are on opposite sides of the carbon to carbon double bond.
What properties are different in geometric isomers?
physical
Rhodopsin needs to convert to trans-rhodopsin under light (a key process in human vision).
How do cis and trans isomers interconvert?
The double bond (pi bond) must break.
What are alkynes?
Unsaturated hydrocarbons with a functional group of (one or more) carbon to carbon triple bonds and a general formula CnH2n-2.
What geometry and bond angle do triple bond carbon atoms have?
Linear geometry and bond angle 180 degrees.
What does a carbon to carbon triple bond consist of?
A sigma bond (2 electrons occupy sigma orbitals) and two pi bonds (4 electrons occupy pi orbitals).
Why are alkynes more reactive than equivalent alkenes and alkanes ?
The second pi bond is weaker than the first pi bond.
Also, the triple bond has higher electron density (than single and double bonds).
