definitions for prelim Flashcards
Molecular orbitals?
Molecular orbitals form when atomic orbitals combine
Pi bonds
Molecular orbitals that form by side-on overlap of parallel atomic
orbitals that lie perpendicular to the axis of the covalent bond.
Sigma bonds
Molecular orbitals that form by end-on overlap of atomic orbitals
along the axis of the covalent bond.
Hybridisation
Hybridisation is the process of mixing atomic orbitals within an atom
to generate a set of new atomic orbitals called hybrid orbitals
sp^3 orbitals
the 2s orbital and the three 2p orbitals of carbon hybridise
to form four degenerate sp3 hybrid orbitals
sp^2 orbitals
The 2s orbital and two of the 2p orbitals hybridise to
form three degenerate sp2 hybrid orbitals
sp orbitals
The 2s orbital and one 2p orbital of carbon hybridise to form two
degenerate hybrid orbitals
HOMO
highest occupied molecular orbital (HOMO)
LUMO
The lowest antibonding
molecular orbital is called the lowest unoccupied molecular orbital
(LUMO).
Chromophore
A chromophore is a group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum
Conjugated system
conjugated system —
a system of adjacent unhybridised p orbitals that overlap side-on to
form a molecular orbital across a number of carbon atoms. Molecules with
alternating single and double bonds, and aromatic molecules have
conjugated systems
Homolytic bond fission
- results in the formation of two neutral radicals
- occurs when each atom retains one electron from the sigma covalent
bond and the bond breaks evenly - normally occurs when non-polar covalent bonds are broken
Heterolytic bond fission
- results in the formation of two oppositely charged ions
- occurs when one atom retains both electrons from the sigma
covalent bond and the bond breaks unevenly - normally occurs when polar covalent bonds are broken
Single headed arrow
a single-headed arrow indicates the movement of a single
electron
Double headed arrow
double-headed arrow indicates the movement of an electron
pair
Nucleophiles
- negatively charged ions or neutral molecules that are electron
rich, such as
Cl^- , Br^- , OH^- , CN^- NH3 and H2O - attracted towards atoms bearing a partial positive or full positive charge
- capable of donating an electron pair to form a new covalent bond
Electrophiles
- positively charged ions or neutral molecules that are electron
deficient, such as H^+ NO2^+ and SO3 - attracted towards atoms bearing a partial negative or full negative
charge - capable of accepting an electron pair to form a new covalent bond
Skeletal formula
skeletal structural formula, neither the carbon atoms, nor any
hydrogens attached to the carbon atoms, are shown
Monohaloalkanes
- contain only one halogen atom
- can be classified as primary, secondary or tertiary according to
the number of alkyl groups attached to the carbon atom
containing the halogen atom
SN1
SN1 is a nucleophilic substitution reaction with one species in the rate
determining step and occurs in a minimum of two steps via a trigonal
planar carbocation intermediate.
SN2
SN2 is a nucleophilic substitution reaction with two species in the rate
determining step and occurs in a single step via a single five-centred,
trigonal bipyramidal transition state
Alcohols
Alcohols are substituted alkanes in which one or more of the
hydrogen atoms is replaced with a hydroxyl functional group, –OH
group
Ethers
Ethers can be regarded as substituted alkanes in which a hydrogen
atom is replaced with an alkoxy functional group, –OR, and have the
general structure R’ – O – R’’, where R’ and R’’ are alkyl groups.
Markovnikov’s Rule
Markovnikov’s rule states that when a hydrogen halide or water is
added to an unsymmetrical alkene, the hydrogen atom becomes
attached to the carbon with the most hydrogen atoms attached to it
already. Markovnikov’s rule can be used to predict major and minor
products formed during the reaction of a hydrogen halide or water
with alkenes.
Amines
Amines are organic derivatives of ammonia in which one or more
hydrogen atoms of ammonia has been replaced by an alkyl group
Benzene
Benzene (C6H6) is the simplest member of the class of aromatic
hydrocarbons. The benzene ring has a distinctive structural formula. The stability of
the benzene ring is due to the delocalisation of electrons in the
conjugated system. The presence of delocalised electrons explains
why the benzene ring does not take part in addition reactions.
Bonding in benzene can be described in terms of sp2 hybridisation,
sigma and pi bonds, and electron delocalisation
Isomers
Molecules that have the same molecular formula but different
structural formulae
Structural isomers
Structural isomers occur when the atoms are bonded together in a
different order in each isomer
Stereoisomers
Stereoisomers occur when the order of the bonding in the atoms is
the same but the spatial arrangement of the atoms is different in each
isomer. There are two types of stereoisomer, geometric and optical.
Geometric isomers
- can occur when there is restricted rotation around a carbon to carbon double bond or a carbon-carbon single bond in a cyclic compound
- must have two different groups attached to each of the carbon
atoms that make up the bond with restricted rotation - can be labelled cis or trans according to whether the substituent
groups are on the same side (cis) or on different sides (trans) of
the bond with restricted rotation
-have differences in physical properties, such as melting point and
boiling point
-can have differences in chemical properties
Optical isomers
- occur in compounds in which four different groups are arranged
tetrahedrally around a central carbon atom (chiral carbon or chiral
centre) - are asymmetric
- are non-superimposable mirror images of each other
- can be described as enantiomers
-have identical physical properties, except for their effect on plane polarised light - have identical chemical properties, except when in a chiral
environment such as that found in biological systems (only one
optical isomer is usually present) - rotate plane-polarised light by the same amount but in opposite
directions and so are optically active - when mixed in equal amounts are optically inactive because the
rotational effect of the plane-polarised light cancels out — this is
called a racemic mixture
racemic mixture
when mixed in equal amounts are optically inactive because the
rotational effect of the plane-polarised light cancels out
Experimental microanalysis
Elemental microanalysis is used to determine the masses of C, H, O,
S and N in a sample of an organic compound in order to determine its
empirical formula.
Mass spectrometry
Mass spectrometry can be used to determine the accurate gram
formula mass (GFM) and structural features of an organic compound.
The mass-to-charge ratio
The mass-to-charge ratio of the parent ion can be used to determine
the GFM of the molecular ion, and so a molecular formula can be
determined using the empirical formula.
Infrared spectroscopy
Infrared spectroscopy is used to identify certain functional groups in
an organic compound
Proton nuclear magnetic resonance spectroscopy
Proton nuclear magnetic resonance spectroscopy (proton NMR or 1H
NMR) can give information about the different chemical environments
of hydrogen atoms (protons or 1H) in an organic molecule, and about
how many hydrogen atoms there are in each of these environments.
High-resolution 1H NMR
High-resolution 1H NMR uses higher radio frequencies
In a high-resolution 1H NMR an interaction with 1H atoms on
neighbouring carbon atoms can result in the splitting of peaks into
multiplets
low-resolution 1H NMR
low-resolution 1H NMR and provides more detailed spectra
Agonist
An agonist mimics the natural compound and binds to the
receptor molecules to produce a response similar to the natural
active compound.
