orgo 1 exam 2

alkane definition

-ane ending

only carbon and hydrogen

all c’s are sp3 hybridized (4 bonds/lone pairs) (only single bonds)

alkane naming formula

prefix (substituents/branches) + parent (how many carbons) + suffix (what functional group) (-ane for alkanes)

alkane parent chain names

1 carbon: methane

2 C: ethane

3 C: propane

4 C: butane

5 C: pentane

6 C: hexane

7 C: heptane

8 C: octane

9 C: nonane

10 C: decane

11 C: undecane

12 C: dodecane

steps to name alkanes

1. find the parent chain (longest continuous carbon chain)

   1. if 2 are the same length, choose the one w/larger number of branches

2. number atoms in parent chain starting at end closest to first branch

   1. if each end is the same distance, choose the one closer to the second branch

3. identify/number substituents based on number of carbons (prefix + -yl)

   1. if 2 off of 1 carbon, both have same number

4. write as 1 word

   1. hyphens separate prefixes and substituents

   2. commas separate numbers

   3. write alphabetically

   4. if 2+ identical substituents, use multiplier prefixes (di, tri, tetra)

complex substituents

number all substituents at point of attachment to parent chain and identify it

substituent is alphabetized according to first letter of its complete name (including numerical prefix) and is set off in parenthesis

conformations and conformer definition

conformations: different arrangements in space of atoms within a molecule due to rotations around single carbon-carbon bonds (C-C) (basically shapes of a molecule) (shapes impact a molecules stability)

conformer: any specific conformation/shape

conformational analysis

study of energies of different conformations

represented with newman projections (viewing the molecule sideways)

newman projections

front carbon: represented with a dot, carbon closer to you

back carbon: represented with a circle, carbon farther from you

eclipsed vs staggered conformation

eclipsed: most stable, all groups line up

staggered: least stable

decahedral angle

aka: θ

angle between the 2 planes

defines conformers

dihedral angles of staggered and eclipsed conformations

staggered: 60, 180, or 360 degrees

eclipsed: 0, 120, or 240 degrees

torsional strain vs steric strain

torsional: slight repulsion between electron clouds in C-H bonds as they pass each other in an eclipsed conformer

steric: when atoms are forced to occupy the same space, repulsion results

H-H eclipsing energy

1.0 kcal/mol

due to torsional strain

H-CH3 eclipsing energy

1.3 kcal/mol

mostly torsional strain, slightly steric strain

CH3-CH3 eclipsing energy

3.0 kcal/mol

torsional and steric strain

CH3-CH3 gauche energy

0.9 kcal/mol

due to steric strain

due to a 60 degree dihedral angle between the largest groups

anti-conformation

a conformation with a 180 degree dihedral angle between the largest groups

energy difference between staggered and eclipsed conformations

staggered: 0kcal/mol (the most stable form)

eclipsed: 3.0 kcal/mol

cycloalkane conformational analysis

ideal angle for sp3 carbon is 109.5 degrees

angle strain

strain that results from the compression of the ideal 109.5 degree angle

non planar conformation

minimized ring strain and torsional strain

makes molecule more stable

cyclopropane

least stable cycloalkane due to angle strain (60 degrees between bonds) and torsional strain

cyclobutane

compared to cyclopropane: reduced angle strain (b/c 90 degrees)

non planar conformation

cyclopentane

no angle strain

envelope strain minimizes torsional strain

5th carbon is above or below the plane

cyclohexane

most stable cycloalkane

no angle or torsional strain

non planar (chair conformation)

most common in nature

cycloalkane stability ranking

least stable: cyclopropane

cyclobutane

cyclopentane

most stable: cyclohexane

why does cyclohexane not exist in boat form

the flagpole H’s IH’s that face up) repel each other and all other H’s eclipse, making it very unstable

chair conformation drawing

arm rest bonds first (parallel and slightly tilted)

head rest (above plane) and foot rest (below plane) carbons added

3 pairs of parallel lines

flipped chair

head rest carbon becomes foot rest

foot rest carbon becomes head rest

both the original and flipped chair conformations have the same energies

hydrogens in chair conformation

axial hydrogen: run vertically, alternate up and down

equitorial hydrogen: run parallel to the arm rest bonds not involved in the vertex, alternate up and down

if axial is up, equitorial is down

if equitorial is up, axial is down

flipped chair: axial become equitorial, equitorial become axial

1, 3-diaxial interaction

gauche interaction between methyl group on carbon 1 and CH2 group on carbon 3

energy is 1.8 kcal/mol (2 × 0.9)

substituted cyclohexane

substituent in equatorial orientation: no energy b/c parallel to bonds

substituent in axial orientation: gauche interaction occurs (CH3-CH2), less stable conformation

consequences of 2 bulky substituents (of at least -CH3) attached to neighboring carbons

1 axial and 1 equatorial: gauche

1 axial and 1 axial: no gauche b/c anti

1 equatorial and 1 axial: gauche

1 equatorial and 1 equatorial: gauche

primary/secondary/tertiary/quaternary carbons

primary: only 1 carbon atom bonded

secondary: only 2 carbon atoms bonded

tertiary: 3 carbon atoms bonded

quaternary: 4 carbons atoms bonded

structural/constitutional isomers vs geometric isomers

structural: same formula, different connectivities

geometric: identical connectivities, different spatial orientation

cis/trans