unit 3 chemistry cover Flashcards
What does the combination of two atomic orbitals result in?
The formation of a bonding molecular orbital and an antibonding orbital. The bonding molecular orbital encompasses both nuclei.
What is the basis of bonding between atoms?
The attraction of the positively charged nuclei and the negatively charged electrons in the bonding molecular orbital.
What happens in a non polar covalent bond?
The bonding molecular orbital is symmetrical about the midpoint between two atoms.
What do polar covalent bonds result from?
Bonding molecular orbitals that are asymmetric about the midpoint between two atoms.
Where are sigma molecular orbitals?
Along the axis of the covalent bond.
Where are pi molecular orbitals?
They lie perpendicular to the axis of the covalent bond.
What are the electrons in the benzene system?
Delocalised.
What is a chromophore?
A group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum.
How can monohaloalkanes form alkenes?
By taking part in elimination reactions using a strong base, such as potassium or sodium hydroxide in ethanol.
What mechanisms can monohaloalkanes take part in for nucleophilic substitution reactions?
SN1 and SN2
What is SN1?
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.
What is SN2?
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.
What is elemental microanalysis used for?
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.
What can elemental microanalysis be determined from?
♦ combustion product masses
♦ percentage product by mass
What can mass spectrometry be used to determine?
The accurate gram formula mass (GFM) and structural features of an organic compound.
What happens in mass spectrometry?
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.
How is a mass spectrum obtained?
Showing a plot of the relative abundance of the ions detected against the mass-to-charge (m/z) ratio.
What is infrared spectroscopy used for?
To identify certain functional groups in an organic compound.
In infrared spectroscopy, what happens?
Infrared radiation is passed through a sample of the organic compound and then into a detector that measures the intensity of the transmitted radiation at different wavelengths.
What can proton nuclear magnetic resonance spectroscopy (proton NMR or 1H NMR) 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.
How do 1H nuclei 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).
What does absorption of radiation in the radio frequency region of the electromagnetic spectrum cause?
The 1H nuclei to ‘flip’ from the lower to the higher energy alignment. As they fall back from the higher to the lower energy alignment the emitted radiation is detected and plotted on a spectrum.
In a 1H NMR spectrum, what is the chemical shift, δ , (peak position) related to?
The environment of the 1H atom and is measured in parts per million (ppm).
How can 1H NMR spectra be obtained?
Using low-resolution or high- resolution NMR.
