Integrated SequencePhysics Chemistry Organic Biology

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Special points of emphasis

The Chemical Bond

Conjugated π Systems and Aromaticity

Reactions of Conjugated Species

Allylic free radicals and allylic cations are reactive intermediates in allylic halogenation and addition of HX to conjugated diene, respectively. These forms are examples of conjugated π electron systems. In these intermediates, electrons are delocalized over a π orbital shared by more than two atoms as the π orbital of the alkene overlaps with the π orbital of the trigonal planar cation or radical.


The Chemical Bond


Chemical Thermodynamics and the Equilibrium State

Conjugated π Systems and Aromaticity

Reactions of Alkyl Halides

Allylic carbocations are more stable than ordinary alkyl carbocations. For example, a tertiary allylic halide is more reactive toward SN1 substitution than a regular tertiary alkyl halide because the vinyl group releases electrons by resonance to stabilize the carbocation.

The Chemical Bond

Conjugated π Systems and Aromaticity

Bioenergetics and Cellular Respiration

Integration of Metabolism


Mammalian Tissues and Histology

Sensory Systems

The Properties of Light

I remember a question from my own MCAT which was basically to identify which of the answer choices was a pigment. Pigments have extended conjugated systems. In pigments, conjugation decreases the energy difference between the highest occupied molecular orbital (HOMO) of the ground state π system and the lowest unoccupied molecular orbital (LUMO). This change enables pigments to absorb light in the visible range. Visible photons are of lower energy than would be typically absorbed by organic molecules. Important pigments in biology include chlorophylls a and b, the cytochromes of the mitochondrial matrix, retinal in vision, and from the laboratory perspective, many of the stains used in histology.

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