Chapter 3 Flashcards
Boiling Point of Alkanes
As the number of carbons in an alkane increases, the boiling point will increase due to the larger surface area and the increased Van der Waal attractions
Melting points of Alkanes
- Melting points increase as the carbon chain increases
- Alkanes with an even number of carbons have higher melting points than those with an odd number of carbons
- Branched alkanes have higher melting points than unbranched alkanes
Methane Representation
- Tetrahedral
- sp3 hybrid carbon with angles of 109.5 degrees
Ethane Representations
- Two sp3 hybrid carbons
- Rotation about the C-C sigma bond
Conformations definition
Conformations are different arrangements of atoms caused by rotation about a single bond
Conformations of Ethane
Pure confomers cannot be isolated in most cases, because the molecules are constantly rotating through all the possible conformations
ethane eclipsed conformation
ethane staggered conformation
Ethane Conformations Energy Diagram
The torsional energy of ethane is lowest in the staggered conformation
Propane Conformations
propane eclipsed conformation
propane staggered conformation
Propane conformation energy diagram
The staggered conformations of propane are lower in energy than the eclipsed conformations. Since the methyl group occupies more space than a hydrogen, there is a greater torsional strain for propane than for ethane.
butane totally eclipsed conformation
butane gauche (staggered) conformation
butane eclipsed conformation
butane anti (staggered) conformation
Steric Strain in Butane
- 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
- This kind of interference between two bulky groups is called steric strain