Alkanes + Cyclo Flashcards
According to old names a propane substituent bonded at the middle is called what?
Isopropyl
What is a primary carbon?
One which is bonded to 1 other carbon
What is a secondary carbon?
One which is bonded to 2 other carbons
What is a tertiary carbon?
One which is bonded to 3 other carbons
What happens to melting/ Boiling points as the carbon chain gets longer and why?
They increase due to stronger London dispersion forces
What are London dispersion forces?
When electrons repel each other creating temporary delta positives and negatives, thus a temporary dipole.
Theyre really weak intermolecular interactions
Do branched alkanes have higher or lower melting boiling points than straight chains?
Lower, they’re harder to pack and therefore experience less temporary dipoles (London dispersion forces)
Are alkanes reactive?
Quite unreactive due to strong c-c
But can have reactions eg with chlorine gas and can be burnt (oxidisation)
Why do we burn alkanes?
The c-c bond is really strong, so when burnt it releases a lot of energy which can be used.
What is a constitutional isomer?
It has a different structural arrangement, different connectivity
What is an molecule isomer?
Different molecules that have the same molecular formula. So can be arranged differently etc
What does a staggered conformation mean?
When atoms are in the form with lowest energy. they face the least repulsion, atoms are as far apart as possible within the molecule
What does an eclipsed conformation mean?
Molecule has rotated in a way in which atoms are overlapping. Electrons repel each other therefore this form is a high energy form
What is the anti conformation?
When the molecule has rotated in a way in which no atoms are overlapping, it has the least repulsion between atoms and is therefore the most stable
What is the gauche conformation?
When the molecule has rotated in such a way that it is staggered but there may be some groups overlapping so it is higher in energy than the anti conformation
How can molecules have rigidity if they are constantly rotating? (eg enzymes)
By creating ring structures, bond ability to rotate is significantly decreased
Why are many enzymes cyclic?
Cyclic bonds are harder to rotate and are therefore more rigid
Are cycloalkanes isomers of the linear version?
No there is normally two less hydrogens, different molecular formula
Why are 6 membered rings the most common?
They experience the least ring strain.
What is torsional strain?
strain in a ring caused by trying to avoid eclipsing. (ring puckers)
What is steric ring strain?
When the bulkiness of the groups causes them to be close
What is angle strain?
When the ring forms angles that deviate from the common carbon tetrahedral 109.5 degrees
What has lower energy the boat or the chair conformation? and why?
Chair has lower energy as the atoms are more staggered, they face less repulsion and are therefore more stable
Why does boat conformation have higher energy than chair?
It has more torsional strain. Groups closer together
What is lower in energy equatorial position or axial?
equatorial as it can be further from other atoms
Why do most rings once in chair conformation normally stay in chair?
It is the lowest energy form, also the energy cost to get to half chair form is really high
What is thermodynamically more stable, CIS or TRANS?
Trans as they are on opposite sides, therefor face less repulsion
What kind of isomers are cis and trans?
Stereoisomers
What is a stereoisomer?
orientation in space is different. Put together in the same way.
What is a constitutional isomer?
Same molecular formula but different connectivity
with a longer chain of alkane is it more or less likely to be solid?
More likely since more intermolecular forces (London dispersion forces)
What is electronegativity?
How good it is at pulling electrons towards itself
Order of strength of forces
Covalent ionic hydrogen dipole-dipole induced-dipole induced-induced (London)
Do branched or linear alkanes have higher melting points?
Linear have higher melting points since they can pack better so more intermolecular forces
Why do spontaneous reactions happen?
products are more stable than reactants so more energy given out then needed to break or make the bonds
