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18 Chapter 1 STRUCTURE AND BONDING IN ORGANIC MOLECULES (3) Same as Also CH₃CH₂OCH₃. Bond-line: O 46. Remember: The most important consideration is the presence of electron octets around as many atoms as possible (except for H, of course). All C, N, and 0 atoms have octets in the structures below. (a) and H₂C=C=CH₂ + (b) and Charges in for N, (5 valence electrons in atom) in bonds) = +1; for C, (4 valence e⁻ in atom) in bonds) in lone (c) CH₃CH and None of the pairs of molecules above consist of resonance forms: In each case the two structures differ in the relative positions of the atoms. Resonance forms differ only in the disposition of the electrons. RR R R 47. (a) (1) R:B:N:R R:B::N:R (2) R:B:O:R R:B::O:R + + R R (3) R:B:F: R:B::F: We use the symbol 'R' here to represent + (b) The octet rule takes precedence over the charge-separation rules, so the double bond-containing structures are preferred in all three cases. (c) In each double-bond-containing structure a positive charge resides on an electronegative atom (F, O, or N). As a result of the electronegativity order F is least able to accommodate a positive charge. Thus, the charge-separated resonance form of R₂BF will be favored to the smallest extent. This resonance form is more favorable in R₂BOR and is even better in R₂BNR₂, because the ability of the electronegative atom to bear the positive charge increases in the order (d) Both are sp² hybridized to accommodate the resonance form with the double bond. 48. Each marked carbon is attached to its three unmarked neighbors in a trigonal planar manner. This arrangement is best explained by sp² hybridization at C*, with the three sp² hybrids engaged in bonding between each C* and its CH₂ neighbors. The σ bond connecting the two C* atoms is perpendicular to each the two C*: planes incorporating the sp² hybrids and results from overlap of the pure p orbitals remaining on C Uses sp² orbital c*-c of marked carbon C Uses orbitals of each marked carbon C c*-c Plane C 120° The usual C*-C* linkage. resulting from overlap of unhybridized p is longer and much weaker than the