(d) Which of the Lewis structures in (a) yields the most

CEM 141 Lecture 28: Lewis Structures Part 2 Dr. Jian Hu November 9 , 2016 Bonding in Hydrocarbons  Deduce the formula for a linear hydrocarbon with 7 carbon atoms (a linear hydrocarbon is a structure with only hydrogen and carbon, and is not a ring structure, or does not contain triple bonds) Answer  C H 7 16 This is because each carbon on the end of the chain can be surrounded by 3 hydrogens, and each carbon in the middle of the chain can be surrounded by only 2, totaling 16  The generic formula for the numbers of carbons and hydrogens in a hydrocarbon: C n 2n+2  If a hydrocarbon does not satisfy this formula, it likely has double bonding  Example: C 2 4Ethylene)  each carbon is sp hybridized, a double bond exists 2 between the carbons in the form of one sigma bond (between sp orbitals) and one pi bond (overlap of sideways p orbitals)   While sigma bonds can rotate freely, pi bonds cannot   Are these molecules the same  They are not the same, because the C-C double bond cannot be rotated since it contains a pi bond In a cis molecule: carbons are on the same side In a trans molecule: carbons are on opposite sides  Pi bonds actually can be rotated, but only when large amounts of energy are added (usually in the form of heat)  Biochemistry application: vision  input energy from light changes cis iso