Part 1 Flashcards
Alkynes
Cn H2n-2 (triple bond)
Physical properties are similar to alkenes and alkanes.
Shorter = gases, boiling at high T than alkenes.
Nomenclature
- Multiple bonds should be on backbone.
- -OH is high priority (placed above multiple bond)
- Haloalkanes, ethers, and ketones are often given common names (e.g. methyl chloride, diethyl ketone)
- Aldehydes/carboxylic acids are terminal functional groups
- Specify isomer, if relevant (such as cis/trans, R or S, etc).
Isomers
Chemical compounds that have same molecular formula, but differ in structure.
May be extremely similar or extremely different.
Structural Isomers
Share only their molecular formula, but their atomic connectivity is different.
Therefore, they may have very different chemical and physical properties.
Stereoisomers
Have same atomic connections, but the atoms are arranged differently in space.
Examples:
Geometric isomers, Enantiomers, Diastereomers, Meso Compounds, and Conformational.
Chirality
Carbon atoms have four different substituents.
Geometric Isomers
Differ in position of substituents attached to a double bond.
Cis (Z) - Substituents on same side (based on high atomic number)
Trans (E) - Substituents are on opposite sides.
Enantiomers
Chiral objects that are non-superimposable mirror images.
Specific type of stereoisomers.
Absolute Configuration
(R) and (S) notation.
- Think of a steering wheel.
- Lowest priority substituent is in fourth position and should point away from you, down the column.
- While #1, 2, and 3 lie on the wheel itself.
- R is clockwise, and S is counterclockwise.
Fischer Projection
Horizontal lines indicate bonds that project from plane of page, while vertical lines behind plane of page.
Racemic mixture
Mixture of equal concentrations of both the (+) and (-) enantiomers.
Rotations cancel each other out, thus NO optical activity.
Diastereomers
Differ in chirality, but are NOT mirror images.
For any molecule with n chiral centers, there are 2^n possible stereoisomers.
e.g. Compound with 2 chiral centers = 4 stereoisomers.
Meso Compounds
Have a mirror image that is superimposable.
Thus, NOT optically active.
Have a mirror plane of symmetry
Conformational Isomers
Differ only by rotation about one or more single bonds.
Analogous to a person sitting or standing.
Can be seen in Newman projection.
Newman Projection
Line of sight extends along a carbon carbon bond axis. (Gauge, anti, eclipsed versions)
Straight-Chain Conformations
gauche < eclipsed < totally eclipsed
anti isomers have lowest energy
totally eclipsed have highest energy
At RT these easily interconvert
Cyclic Conformations
Strain Energy is due to ring strain, angle strain, torsional strain, and nonbonded strain (van der waals)
Chair and boat conformations are most important forms of cyclohexane. Chair is most stable and lowest energy.
Axial Substituents
Axial substituents are on Vertical Axis, like axial skeleton.
Axial is NOT favored.
Equatorial Substituents
Equatorial substituents go around the middle, like earth’s equator.
Equatorial is favored over axial.
A bulky substituent can prevent the ring from adapting certain conformations.
Hybridization
Concept of mixing atomic orbitals to form new hybrid orbitals.
Useful in explanation of shape of molecular orbitals.
Bonding Summary (single, double, and triple bonds)
Single bonds: sigma, sp^3, 109.5 degrees
Double bonds: sigma/pi, sp^2, 120 degrees
Triple bonds: sigma/pi/pi, sp, 180 degrees
Free Radical Halogenation
One or more H atoms are replaced by halogen atoms (Cl, Br, or I) via free radical substitution. Occurs in Alkanes.
Three steps:
- Initiation
- Propagation
- Termination
Bromine is slow and picky and attacks most substituted.
Chlorine is rapid and attacks primary H with abundance.
Combustion
Occurs in Alkanes.
Reaction of alkanes with molecular oxygen.
Forms CO2, Water, and Heat (desired product)
Pyrolysis
Occurs in Alkanes.
Also called cracking”.
