Indicate True(T) orFalse (F) for each of the following statements: (a) The tempo
ID: 691347 • Letter: I
Question
Indicate True(T) orFalse (F) for each of the following statements:
(a) The temporary molecular shape that resultsfrom rotation of groups about single bonds is
called a conformation of amolecule.
(b) The eclipsed conformation of ethane ismore stable than the staggered conformation.
(c) The phenomenon of electron delocalization(via orbital overlap) from a filled bondingorbital
to an adjacent unfilled orbital is calledhyperconjugation.
(d) The barrier to rotation about a singlebond is called the torsional barrier of thatparticular
single bond.
(e) The factors involved in the rotationalbarrier about a carbon-carbon single bond aretogether
called torsional strain.
(f) Considering the rotation about the C2-C3bond of butane, the gauche conformation is more
stable than the anti conformation.
(g) The heat of formation of a hydrocarbon isthe enthalpy (H) change for the complete
oxidation of the hydrocarbon to carbon dioxideand water.
(h) Cyclobutane has a greater stain energycompared to cyclohexane.
(i) The C-C-C bond angles in cyclohexane areapproximately 109.5o.
(j) The diaxial conformation ofcis-1,3-dimethylcyclohexane is more stable than thediequatorial
conformer.
Explanation / Answer
(a) The temporary molecular shape that results fromrotation of groups about single bonds is calleda conformation of a molecule.
True (definition)
(b) The eclipsed conformation of ethane ismore stable than the staggered conformation.
False --> Staggered morestable.
(c) The phenomenon of electrondelocalization (via orbital overlap) from a filled bonding orbitalto an adjacent unfilled orbital is calledhyperconjugation.
True. specifically sigma orbitals to emptypi generally
(d) The barrier to rotation about a singlebond is called the torsional barrier of that particular singlebond.
I learned it as rotational barrier... (andthat's what the next statement says?) -->False
(e) The factors involved in the rotationalbarrier about a carbon-carbon single bond are together calledtorsional strain.
Hm. I'm not sure about the terminology,check your book?
(f) Considering the rotation about theC2-C3 bond of butane, the gauche conformation is more stable thanthe anti conformation.
False, anti is more stable by about 4kJ/mol
(g) The heat of formation of a hydrocarbonis the enthalpy (H) change for the complete oxidation of thehydrocarbon to carbon dioxide and water.
False, that would be heat ofcombustion
(h) Cyclobutane has a greater stain energycompared to cyclohexane.
True (assuming strain and not stain)--> compare angles to those of other tetrahedralmolecules
(i) The C-C-C bond angles in cyclohexaneare approximately 109.5o.
True, tetrahedralcarbons
(j) The diaxial conformation of cis-1,3-dimethylcyclohexane ismore stable than the diequatorial conformer.
False, 1,3 diaxial interactions with hydrogen atoms =greater strain