Molecular Orbitals and Hybridisation Flashcards
Organic Chemistry
where do the electrons of opposite spin spend most of their time between the two nuclei?
the bonding orbital
how are sigma bonds formed?
end-on-end overlapping of orbitals
how are pi bonds formed?
side-on-side overlapping of unhybridised p-orbitals
why are sigma bonds stronger?
they are very efficient at overlapping so have much stronger bonds
what type of compounds are colourless?
saturated compounds that contain only sigma bonds
what is a chromophore?
a group of atoms in a molecule that is responsible for the absorption of light in the visible range, and therefore its colour
organic molecules that are coloured have alternating double and single bonds in long chains, what is this called?
conjugated system
what can be said about the size of the conjugated system and the energy difference between the HOMO and LUMO?
the larger the conjugated system(the greater number of atoms with delocalised electrons), the smaller the energy gap between the HUMO and LUMO.
what are the two ways in which electrons can be redistributed?
homolytic and heterolytic fission
what is homolytic fission?
the breaking of a covalent bond to produce two free radicals.
what is heterolytic fission?
when a covalent bond breaks and both of the electrons move to one of the atoms
what is a result of heterolytic fission?
two oppositely charged ions
where is heterolytic fission most likely to occur?
in polar molecules
which atom do both of the electrons tend to go to?
the more electronegative atom
what is the term used to describe the positively charged carbon atom?
carbocation
what is the term used to describe the negatively charged carbon atom?
carbanion
what does the double-headed curly arrow show?
the movement of two electrons being redistributed
what is a nucleophile?
a molecule or negatively charged ion that have at least one lone pair of electrons (lone-pair donor)
how do nucleophiles work?
the negatively charged ion/group is attracted to an electron-deficient centre, where it donates its electron pair to form a new covalent bond.
four examples of nucleophiles:
*H20
*NH3
*OH-
*halide ions
what is an electrophile?
a positively charged ion or neutral molecule that are electron deficient-accept a pair of electrons
three examples of electrophiles:
*H2O+
*NO2+
*SO3
how do electrophiles work?
they are attracted towards an area of high electron density with a negative or partial negative charge
what is a substitution reaction?
when an atom or group of atoms is replaced (substituted) for another atom or group of atoms
