neighboring group participation - 2026 ACF Regionals

Question

This phenomenon can explain why acetolysis rates for exo-substituted 2-norbornanes are 350 times greater than those for endo-substituted isomers. For 10 points each:

[10h] Name this phenomenon where a reaction center interacts with a non-conjugated lone pair or bonding electrons in the same molecule. A classic example of this phenomenon is the elevated SN2 rates for nitrogen mustards.

ANSWER: neighboring group participation [or NGP; accept anchimeric assistance]

[10m] In another example of NGP, pi electrons stabilize the 2-norbornyl one of these species, which George Olah isolated using magic acids. These species migrate to achieve more stable configurations in hydride or methyl shifts.

ANSWER: carbocations [accept carbenium ions; accept carbonium ions; prompt on cations or ions]

[10e] The 2-norbornyl cation can be described non-classically using bonds consisting of two electrons distributed over this many centers. Banana bonds are used to model cyclopropane, which has this many carbon atoms.

ANSWER: three [accept three-center two-electron bonds]

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Summary


California (North)	Main Site	Y	3	16.67	100%	67%	0%
California (South)	Main Site	Y	4	10.00	75%	25%	0%
Canada	Main Site	Y	11	14.55	91%	46%	9%
Florida	Main Site	Y	3	3.33	33%	0%	0%
Great Lakes	Main Site	Y	5	18.00	100%	80%	0%
Lower Mid-Atlantic	Main Site	Y	9	8.89	56%	33%	0%
Midwest	Main Site	Y	8	13.75	88%	38%	13%
Northeast	Main Site	Y	5	16.00	100%	40%	20%
Overflow	Main Site	Y	3	13.33	67%	67%	0%
South Central	Main Site	Y	2	10.00	50%	50%	0%
Southeast	Main Site	Y	8	10.00	63%	38%	0%
UK	Main Site	Y	6	10.00	67%	33%	0%
Upper Mid-Atlantic	Main Site	Y	9	13.33	89%	44%	0%
Upstate NY	Main Site	Y	4	5.00	50%	0%	0%

Data


Berkeley B	Berkeley A	0	10	10	20
Berkeley C	Berkeley D	0	10	10	20
Stanford A	Stanford B	0	0	10	10
McGill B	Brock	0	0	10	10
Toronto E	Guelph	0	0	10	10
McGill A	Waterloo B	0	0	10	10
McMaster A	Queen's	0	10	10	20
Florida C	Central Florida B	0	0	10	10
Florida A	Central Florida A	0	0	0	0
Central Florida C	Florida B	0	0	0	0
Michigan A	Ohio State B	0	0	10	10
Michigan B	Michigan State	0	10	10	20
CWRU A	Michigan C	0	10	10	20
Ohio State A	Ohio State C	0	10	10	20
CWRU B	Pittsburgh	0	10	10	20
Liberty A	North Carolina B	0	0	0	0
NC State A	Liberty B	0	0	10	10
North Carolina A	Duke	0	0	10	10
Virginia Tech A	North Carolina C	0	10	10	20
South Carolina B	James Madison B	0	0	10	10
South Carolina A	Virginia Tech B	0	10	10	20
Virginia	James Madison A	0	10	0	10
Wake Forest	NC State B	0	0	0	0
William and Mary	VCU	0	0	0	0
UCLA B	Arizona State	0	0	10	10
UCSD C	UC Santa Barbara	0	0	10	10
UC Irvine	UCLA A	0	0	0	0
UCSD B	UCSD A	0	10	10	20
Ottawa	Toronto B	0	10	10	20
Toronto D	Toronto Metropolitan	0	0	10	10
McMaster B	Toronto F	0	0	10	10
Waterloo A	UBC A	10	10	10	30
UBC B	Carleton University	0	10	10	20
Western A	Western B	0	0	0	0
Toronto G	Western C	0	10	10	20
Illinois A	Chicago B	10	10	10	30
Chicago E	Chicago A	0	0	10	10
Indiana C	Illinois C	0	0	0	0
Northwestern B	Indiana B	0	10	10	20
Notre Dame A	Northwestern C	0	10	10	20
Northwestern D	Chicago D	0	0	10	10
Notre Dame B	Purdue A	0	0	10	10
Chicago C	Purdue B	0	0	10	10
Dartmouth A	Brandeis A	0	0	10	10
Brandeis B	Harvard B	0	0	10	10
Brown	Dartmouth B	0	10	10	20
Harvard A	Southern Connecticut State	10	10	10	30
MIT	Yale	0	0	10	10
Missouri B	Carleton College	0	0	0	0
Minnesota A	Georgia Tech A	0	10	10	20
Murray State A	Texas A&M A	0	0	0	0
Texas B	Texas A	0	10	10	20
Bruin	WashU A	0	0	0	0
Georgia Tech C	Georgia Tech B	0	10	10	20
Louisville B	Alabama A	0	0	10	10
Mississipi State	Alabama B	0	0	10	10
Tennessee A	Georgia Tech D	0	0	10	10
Tennessee B	Sewanee	0	0	0	0
Louisville A	Vanderbilt B	0	10	0	10
Kentucky	WashU B	0	10	10	20
Claremont	Washington B	0	10	10	20
City St. George's	Cambridge B	0	0	0	0
Bristol	Edinburgh B	0	0	10	10
Imperial C	Oxford A	0	0	0	0
Durham	Oxford B	0	0	10	10
Imperial A	UCL	0	10	10	20
Maryland B	Catholic	0	10	10	20
Columbia C	Rutgers B	0	10	10	20
Georgetown	Swarthmore	0	0	10	10
Rutgers A	Maryland C	0	10	10	20
NYU C	Vassar	0	0	10	10
John Jay	Johns Hopkins B	0	0	0	0
Columbia A	Johns Hopkins A	0	0	10	10
NYU A	Maryland A	0	0	10	10
Columbia B	NYU B	0	10	10	20
Cambridge C	LSE	0	10	10	20
Binghamton A	Binghamton B	0	0	0	0
Cornell B	Cornell A	0	0	0	0
Cornell C	Rochester	0	0	10	10
Penn State	RIT	0	0	10	10