Flashcards in Organic Chemistry- Isomers Deck (113)
What is an important way to distinguish between molecules?
By identifying isomers of the same compound
What are isomers?
Those that have the same molecular formula but different structures
Can a molecule be an isomer by itself?
Structural isomers are what?
The least similar of all the isomers
What's another anme for structural isomers?
Structural isomers have different what?
Chemical and physical properties
What are physical properties?
Characteristics of processes that don't change the composition of matter, such as melting point, boiling point, solubility, odor, color and density
What are Chemical properties?
Do with the reactivity of the molecule with other molecules and result in changes in chemical composition.
In organic chemicstry, the chemical properties are dicatated by what?
the functional groups in the molecule
How small are the conformational interconversion barriers?
19 kcal/mol between anti staggered butane and totally ecliped butane
Are conformational interconversion barriers easy to overcome?
Yes at room temperature.
However, at very low temperatures, conformational interconversions will dramatically slow. if the molecules do not possess sufficient energy to cross the energy barrier, they may not rotate at all (as happens to all molecules at absolute zero).
Are cycloalkanes fairly stable compounds or fairly unstable?
Both depending on the ring strain
What are the three factors that ring strain arises from?
When does angle strain results?
When bond angles deviate from their ideal values by being stretched or compressed
When does torsional strain resullt?
When cyclic molecules must assume conformations that have eclipsed or gauche interactions.
When does nonbonded strain result?
(Van der Waals repulsion) results when nonadjacent atoms or groups compete for the same space
Nonbonded strain is the dominant source of ______ in the _______.
Steric strain in the flagpole interactions of the cyclohexane boat conformation.
To alleviate strain, cycloalkanes attempt to adopt what?
Various nonplanar conformations.
What are the different shapes that cyclobutane, cyclopentane, and cyclohexane adopt when under strain?
Cyclobutane: puckers into a slight V
Cyclopentane: Adopts an envelope conformation
Cyclohexane: goes into three- chair, boat, twist or ske-boat.
What is the most common cyclokane seen on the MCAT?
What is the most stable conformation of cyclohexane? Why?
The chair, which minimizes all three types of strain
What are axial hydrogen atoms?
Hydrogen atoms that are perpendicular to the plane of the ring (sticking up or down)
What ar eequatorial hydrogen atoms?
Those parallel (sticking out)
In a chain, what do the axial and equatorial orientations do?
Alternate around the ring, that is, if the wedge on C-1 is an axial group, the dash on C-2 will also be axial, the wedge on C-3 will be axial and so on.
Cyclohexane can undergo what?
A chair flip, in which one chair form is converted to the other
During chair flip, cyclohexane passes through which conformation?
After chair flip, what happens?
All axial groups become equatorial and all equatorial groups become axial. All dashes remain dashes, and all wedges remain wedges.
The interconversion of cyclohexane from one chair to the next can be slowed how?
If a bulky group is attached to the ring
Tert-butyl groups are classic examples
For substituted rings, the bulkiest group will fabor what position?
The equatorial position to reduce nonbonded strain with the axial groups in the molecule