Lecture 4: newman, cyclos etc Flashcards
true or false: 2 groups bonded by a double bond can rotate around the bond and get difference conformations
false, but be single
what are conformations
different spacial arrangements of a molucle that are generate by rotation about single bonds
true or false, you can rotate around pie bonds
false, only sigma
explain the relationship between different conformations and their stability
diff conformations are possible but not all have the same energy (some are more stable than others)
=rotating changes the proximity of electrons to each other therefore affecting bond length and energy
explain staggered conformation
where the dihedral angle b/w bonds at each carbon are 180 degrees from each other and groups attached to c are as far away as possible
explain eclipsed formation
atoms bonded to carbons at each end of carbon bond are directly opposive to eeach other and dehidral angle is 0
what is the dihedral angle of staggered
18-
what is the dihderal angle of escliped
0
the H-C-C-H bonds are called what
dehidral
what is anti conforatkon
staggered with didegrealk angles of 18
what is gauche conformation
dihedral angle of 60 betweeen H-H
what conformation has lowest energy
staggered (anti)
what conformation has highest energy
ecliped (total)
explain why staggered anti is the most stable
because there is less steric interactions
we are putting the molecuels are far as possible therefore less e e repulsion/interaction
and hyperconjuation
what is hyperconjugation
favourable overal between filled and unfilled sigma orbitals in stagged conformation
=occurs ehn electrons in filld bonding orbitals move partially into unoccupied anto bonding portion
hyperconjugation is greatest in what configuration
staggered anti
the 2 orbitals are parallel
what is a steroisomer
same molecular formula and connectivity but different arrrangement of atoms in space
what is a constitutional isomer
same molecular formula but diff connectivity
what is a conformational isomer
related to one another by BOND rotation
true or false: cyclopronane doesnt have ring strain
false, it has alot
what is angle strain
deviation from ideal bond angled fue to inherent constraints (rings, size)
explain why cyclopropany is not stable in ring
because normally carbons of alkanes are sp3 hybridized therefore their bond angles should be around 109 but with cyclopropane, internal angles are 60 ttherefore there is alot of angle strain
=poor overalap in sp3 orbitals
=c-c bonds are weak and not as stable
what is the most stable cylco and why
cyclohexeme because internal angles do not differ alot from nomral bond angle
what conformation does cyclohexene adopt to minimize ring sdtraign
chair
what are the axial protons
protons that point up and doen
what are equitorial protons
point away laterall
is there less steric interaction in equirotal or axial
equi
but the different conformations of cyclohexane in decreasing order of stability
chair, twist boat, boat, half chair
what happens to axial and equitoral protons are we change conformations
axial goes to equi and vice versa
which is more stable and why: boat or chair
chair (less sterial interactions)
chair conformatios with larger subs at the axial opr equitoral are more stable
equi because no 1,3 diaxiual intereactions
true or fals: there are less repulsive forced in the axial methyl conformtionl
false, in equi
what are egeometric/cis-trans isomers
they have same moculecular formula, same connectivity but different arrangement of their atoms in space due to presence of double bond
true or false: geometric (cis trans) insomeers are also consideered stereosiomers
true
cis isomers have subsitutents on same or diff side
same
trans insomers have substituents or same or diff sides
diff
which conformation, cis or trans, alllows for dipole moment
cis
all axial subsituents are trans or cis to each other
trans
what is another name for index of hydrogen deficiency
degree of unsaturaion
what is IDH
diff in # of pairs of hydrogen attoms between compound of interest in compairson to normal alkane with same number of C
what is a saturated hydrocarbon
every H is attached to an H (no rings or double bonds)
what is an unsaturated hydrocarbon
C os attached to something that is not a H (double bond, rings)
what is the general molecular formula for alkana
cn h2n+2
minus 2 h for every double bond or ring
what is the formula for a cyclioc alkene
cnh2n-2
what is the formula for alkene or cyclic alkane
cnh2n
1 ring is how many degree of unsaturation
1
1 double bond is how many degree of unsat
1
2 double bonds, is how many degree unsaturation
2
1 triple bond is how mnay degree unsaturation
2
2 rings is how many degrees of unsaturation
2
how to count IHD for halogents
count halogens as tho they are hydrogens
how to count IHD for oxygen
ignore the oxygen atoms and calcualte IHD from remainder of the formula
how to count IDH for nitrtogen
subtract one hydrogen for each nitrogen atom and ignore the nitron atoms
