IUPAC rules for nomenclature
* the longest carbon chain with the most substituents determines the base name
* the end carbon closet to a carbon with a substituent is always the first carbon. in the case of a tie, look to the next substituent
* any substituent is given the same number as its carbon
* if the same substituent is used more than once, use the prefixes di-, tri-, tetra, and so on
* order the substituents alphabetically (ignore prefix)
when the bonding pair of electrons are localized directly between the two bonding atoms.
four rules for resonance
1) atoms must not be moved. move electrons
2) number of unpaired electrons must remain constant
3) resonance atoms must lie in the same plane
4) only proper Lewis structures allowed
two conditions must exist for resonance to occur
1) a species must contain an atom either with a p orbital or an unshared pair of electrons
2) that atom must be single bonded to an atom that posses a double or triple bond.
planar monocylic rings with 4n+2 pi-electrons) should be aromatic (display resonance)
occurs when the center of positive charge on a molecule does not coincide with the center of negative charge.
can be induced in an otherwise nonpolar molecule by a polar molecule, ion, or electric field.
instantaneous dipole moment
can exist in an otherwise nonpolar molecule. arise because the electrons in a bond move about the orbital, and at any given moment may not be distributed exactly between the two bonding atoms even when the atoms are identical.
occur solely due to dipole moments. generally about 1% as strong as covalent bonds.
London Dispersion Forces
the weakest dipole-dipole force is between two instantaneous dipoles. weak, but responsible for phase changes
the only way to physically describe the orientation of atoms around a chiral center.
1) number atoms attached to the chiral center from highest to lowest priority. largest atomic weights are given the highest priority
2) if two atoms have the same element, then their substituents are sequentially compared in order of decreasing priority until one of the substituents is found to have a greater priority than the corresponding substituent on the other carbon.
3) substituents on double and triple bonds are counted two and three times respectively
4) make lowest priority group face away, and see which direction highest to lowest
not related to absolute configuration. molecules have the same _____ _____ about a carbon if they differ by only one substituent and the other substituents are oriented identically about the carbon. this orientation is inverted in an Sn2 reaction.
the resulting light from a polarimeter consists of photons with their electric fields oriented in the same direction.
no rotation of the plane or electric field by a typical compound. may be compounds with no chiral center
the direction and number of degrees that the electric field in plane-polarized light rotates when it passes through a compound is called that compounds ____ ____.
simply a standardized form of observed rotation that is arrived at through calculations using observed rotation and experimental parameters.
have the same molecular formula, have the same bond-to-bond connectivity, are mirror images of each other, but are not the same molecule. must have opposite absolute configurations at each chiral carbon.
rotate plane polarized light in opposite directions
aside from reactions with plane-polarized light and with other chiral compounds, have the same physical and chemical properties.
the ratio of pure enantiomer to racemic mixture. optical purity equals ___ ____ for any mixture of enantiomers
have the same molecular formula, have the same bond-to-bond connectivity, are NOT mirror images to each other, and are not the same compounds.
exist due to hindered rotation about a bond. rotation may be hindered due to ring structure, double or triple bond. have different physical properties.
molecules with same side substituents. have dipole moment. stronger intermolecular forces leading to higher boiling points. less symmetry so fewer crystals, thus lower melting points.
substituent groups in the cis position may crowd each other. produces higher energy levels resulting in higher heats of combustion.
system to describe geometric isomers unambiguously
two substituents on each carbon are prioritized by atomic weight. labeled E or Z.
maximum number of optically active isomers in a single compound.
2ⁿ, where n is the number of chiral centers.
two chiral centers in a single molecule may offset each other. have a plane of symmetry through their center which divides them into two halves that are mirror images of each other. achiral and optically inactive.
if a ring closure occurs at the epimeric carbon, two possible diastereomers called ______. distinguished by the orientation of their substituents. α and β.
vertical lines are assumed to be oriented into the page. horizontal lines are assumed to be oriented out of the page.
a view straight down the axis of one of the σ-bond. both the intersecting lines and the large circle are assumed to be carbon atoms.
index of hydrogen deficiency
indicates the number of pairs of hydrogens a compound is required in order to become a saturated alkane.