Structure and Stereochemistry of Alkanes Flashcards
Relation between boiling points of alkanes and the number of carbons in the compound
Directly proportional, due to the increase in surface area and the increase in van der waals attraction
Which compound has a higher boiling point branched or unbrached alkanes?
Branched, due to the larger surface area
Bonds in the compounds (weakest to the strongest)
London
Dipole - dipole
H bond
Dipole - ion
Type of bond in methane
London
Non polar
Relation between melting point of alkane and the number of carbons in alkane
Directly proportional
True or false
Alkanes with an even number of carbon atoms have higher melting points than with an odd number of carbon atoms
True
Because they are more compacted
Difference between cracking and hydrocracking
Hydrocracking only results in the formation of alkanes (used as fuels), while cracking result in the formation of alkanes and alkenes
Both reactions happen in the presence of catalyst and heat
Conformations
different arrangements of atoms caused by rotation about a single bond.
Steric strain
The totally eclipsed conformation is higher in energy because it forces the two end methyl groups so close together that their electron clouds experience a strong repulsion.
Physical properties of cycloalkanes
• Non-polar (used as solvents)
• Relatively inert
• Boiling point and melting point depends on the molecular weight.
Geometrical isomers
Alkyl group on different carbons
Only two alkyl groups
Cis
Both substituents are up or down
Trans
One substituent is up, the other is down
Ring strain
Angle strain
Torsional strain
Angle strain
The angle is not equal to 109.5°
Torsional strain
when all the bonds are eclipsed
Cyclopropane ring strain
Angle 60
Torsional strain
Cyclobutane ring strain
Planar
Angle 90°
Torsional strain
Non planar
Angle 90°
Less torsional strain
More stable
Cyclopentane
Angle 108°
Non planar
Less torsional strain
More stable
