to memorise by sat Flashcards
Explain formation of molecular orbitals
In atoms electrons occupy atomic orbitals, electrons in molecules occupy molecular orbitals. Molecular orbitals are generated by combining atomic orbitals. The number of orbitals formed is equal to the number of atomic orbitals that combine. Each molecular orbital can hold two electrons.
What are bonding molecular orbitals/antibonding molecular orbitals
One of the molecular orbitals is law and energy than either of the Tomich orbitals that combined to produce it, this is called a bonding molecular orbitals. The other molecular orbital is known as an anti bonding molecular orbital and is of higher energy than either of the atomic orbitals that combined to produce it.
Difference between the bonding molecular orbital is polar/non-polar molecules
In a nonpolar molecule, the molecular orbital will be symmetrical around the two atoms. In a polar molecule, the molecular orbital will be asymmetric around the two atoms.
Sigma bonds and their formation
Molecular orbital is formed by an Overlap of atomic orbitals along the axis of the bonds. I.e. a covalent bond, called a sigma bond. This is usually referred to as an end on overlap.
Pi bonds
To parallel P atomic orbitals that are perpendicular to the axis of the bond can overlap laterally or side on to form a pi bond. The overlap of atomic orbitals is much less effective than the end of overlap. Pie bonds are weaker than Sigma bonds.
What is hybridisation of orbitals
Hybridisation is the process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. Which are degenerate
Hybridisation of alkanes
In alkanes the four sp3 orbitals on each carbon atom will overlap and end on with four other orbitals, i.e. then the hydrogen ___ orbitals and one sp3 orbital on the other carbon atom. Four sigma bonds will be formed and they will adapt a tetrahedral arrangement.
Hybridisation of alkenes
In alkenes, the 3 sp2 orbitals adapt a trigonal planar arrangement. In Ethene each carbon atom uses its three sp2 orbitals two form Sigma bonds with two hydrogen atoms and with other carbon. The unhybridized 2p orbital left on the carbon atoms overlaps the side to form a pi bond.
Hybridisation of alkynes
In alkynes the 2 sp2 orbitals in each carbon form sigma bonds with the other carbon atom. The unhybridized 2p orbitals overlap side on to form pi bonds
Hybridisation of benzene
In benzene, c6h6, each carbon atom is sp2 hybridised and the 3 half-filled sp2 orbitals form sigma bonds with a hydrogen aion and the two neighbouring carbon atoms. This leaves an electron occupying a p-orbital on each carbon atom. Each of there p-orbitals overlap side on with p orbitals on neighbouring carbon atoms, a pi electron bond is formed
What is a chromophore
A chromophore is a group of atoms within a molecule which is replicable for absorption of light. Chromophores Exist in molecules, with conjugated system brackets attract double bonds. Delocalised electrons between atoms are conjugate system has alternating sigma and pi bonds
Why some organic molecules appear coloured
Absorption of electromagnetic energy can cause electrons to be parallel from the highest occupied molecular orbital ‘homo’ to the coho. If the wavelength of light absorbed lies in the ems then the color observed will be complementary to that absorbed
Why most organic molecules are colourless
Most organic molecules are colourless as the gap between the homo and lumo is large, this means that light from uv region is absorbed and so molecule appears colourless
What happens to the frequency of light absorbed when the conjugated system contains more atoms?
If there are more atoms in the conjugated system then there is a smaller energy gap between homo/lumo. Therefore lower frequency and lower energy is absorbed.
what is an isomer
An isomer is a molecule with the same molecular formula but different structural formula
What is a stereoisomers
A stereoisomer is when the order of bonding in each atom is the same but the spatial arrangement of the atom is different in each bond
What are geometric isomers
A geometric isomer occurs when the arrangement of the atom is different in each isomer
Under what circumstances do geometric isomers occur
Occur when there is rotation around a carbon to carbon double bond, also there must be two different groups attached to each of the carbon atoms that make up the bond
What is meant by cis and trans
Cis is groups on the sdame side of the double bond, trans is groups on opposite side of the double bond
How do properties of geometric isomers differ
Geometric isomers can have different physical properties
What are optical isomers
They contain the same number and kinds of atoms and bonds, they are non-super imposable mirror images
When do optical isomers occur
When four different groups are arranged tetrically around a central carbon atom (chiral carbon)
How do properties of optical isomers occur
Identical but on light
Effect of enantiomers on polarise light
One enantiomer will rotate light in one direction and the other enantiomer in the opposite direction by the same difference. as there is an equal amount of each enantiomer, the rotation would cancel
What is a racemic mixture and why are they described as being optically inactive
A racemic mixture is an equal mixture of enantiomers, of a chiral molecule
What is infrared spectroscopy used for
Its used to identify specific functional groups in organic molecules
Explain how infrared spectroscopy works
Infrared spectroscopy intakes infrared at organic molecules which causes their bonds to vibrate in different ways. The wavelengths which are absorbed depend on the type of chemical bondand the atoms at the end of these bonds
What is the general rule regarding the weight of atoms and bond strength
Lighter atoms are converted by stronger bonds (higher energy radiation absorbed), heavier atoms are connected by weaker bonds (lower energy radiation absorbed)
What is nass spectroscopy used for
Mass spectroscopy is used to determine the accurate molecular mass and structural features of a compound
How does mass spectroscopy work
A small sample of an organic compound is bombarded by high energy electrons. This removes electrons from the organic molecule generating positively charged molecular ions known as parent ions. These molecular ions then break into smaller positively charged ion fragments
Explain how proton nmr spectroscopy works
Nuclei of atoms behave like tiny magnets and in a strong magnetic field some align with the field (lower energy) whilst the rest align against it (higher energy). The absorption of radiation in the radio frequency of the electromagnetic spectrum causes the 1h nuclei to flip from the lower to higher energy alignment. As they fall back from higher to lower energy alignment emitted radiation is detected and plotted on a spectrum
How are proton environments identified
The fragments
What is homlytic fission
The neutral species are formed and each species has an unpaired electron so is a free radical. I single headed curly arrow is used. Not useful in synthetic chemistry as complex mixture of products form due to the chain reaction
what is heterolytic fission
Normally occurs when polar covalent bonds are broken, the more electronegative atom retains both electrons. A double headed curly are all as used as pair of electrons are moving.
