Double bond rule

The double bond rule states that chemical elements with a principal quantum number greater than 2 (e.g. Period 3 elements and lower) do not form multiple bonds (e.g. double bonds and triple bonds) with themselves or with other elements.^[1] The double bonds if they exist are weak due to weak pi bonds as a results of poor orbital overlap.

This rule was challenged and ultimately made obsolete starting from 1981 with the discovery of silicon and phosphorus double bonds.^[2] Double bonds that would ordinarily not form can be stabilized with proper functional groups either electronically or sterically (kinetic stabilization).

Double bonds for carbon and nearest neighbours
	boron	carbon	nitrogen	oxygen	silicon	phosphorus	sulfur
boron	diborenes	alkylideneboranes	aminoboranylidenes rare [3]	oxoboranes rare, rapid oligomerization [4]	not known	boranylidenephosphanes, rare, stable compounds are known [5]	thioxoboranes , rare [6]
carbon		alkenes	imines	carbonyls , oxonium ions	silenes	phosphaalkenes	thioketones
nitrogen			Azo compounds	nitroso compounds	silanimines, rare easy oligomerization, only at low temp. [7]	phosphazene	sulfilimines
oxygen				dioxygen	Silanones Si=O bonds do not form oligomerisation to siloxane, only fleeting evidence [8] [9]	Numerous, e.g. phosphine oxides , phosphonates, Phosphinates, phosphates	sulfinyls
silicon					disilenes	Silylidenephosphanes a.k.a. phosphasilenes rare [10]	silanethiones , rare easy oligomerization [11]
phosphorus						diphosphenes	Common, for example in thiophosphates and in phosphine sulfides for example triphenylphosphine sulfide, certain dithiadiphosphetanes
sulfur							disulfur, thiosulfoxides

References

1. ^ New Element-Carbon (p-p) Bonds Doz. Dr. Peter Jutzi Angewandte Chemie International Edition in English Volume 14 Issue 4, Pages 232 - 245 1975 doi:10.1002/anie.197502321
2. ^ Multiple bonds to silicon: 20 years later Robert West Polyhedron Volume 21, Issues 5-6, 15 March 2002, Pages 467-472 doi:10.1016/S0277-5387(01)01017-8
3. ^ some research efforts exists in isomerization of B=NH₂ to triple bonded iminoborane HBNH The aminoboranylidene–iminoborane isomerization Victor M. Rosas-Garcia and T. Daniel Crawford J. Chem. Phys, 119, 10647 2003
4. ^ Synthesis and Characterization of a Coordinated Oxoborane: Lewis Acid Stabilization of a Boron-Oxygen Double Bond Dragoslav Vidovic, Jennifer A. Moore, Jamie N. Jones, and Alan H. Cowley J. Am. Chem. Soc., 2005, 127 (13), 4566-4567 doi:10.1021/ja0507564
5. ^ For instance Ar*P=B(TMP)2 with TMP = 2,2,6,6-Tetramethylpiperidine and Ar* = 2,6-dimesityl-phenyl Boron-Pnictogen Multiple Bonds: Donor-Stabilized PdB and AsdB Bonds and a Hindered Iminoborane with a B-N Triple Bond Eric Rivard, W. Alexander Merrill, James C. Fettinger, Robert Wolf, Geoffrey H. Spikes, and Philip P. Power Inorg. Chem. 2007, 46, 2971-2978 doi:10.1021/ic062076n
6. ^ Formation and Reactions of a Thioxoborane, a Novel Boron--Sulfur Double-bond Compound Norihiro Tokitoh, Mitsuhiro Ito, and Renji Okazaki Tetrahedron Letters, Vol. 37, No. 29, pp. 5145-5148, 1996
7. ^ Observation of a silanimine in an inert matrix and in solution at low temperature Steven S. Zigler, Robert West and Josef Michl Chemistry Letters Vol.15 , No.6(1986)pp.1025-1028 doi:10.1246/cl.1986.1025
8. ^ On the proposed thermal interconversion of matrix-isolated dimethylsilylene and 1-methylsilene: their reactions with oxygen atom donors Charles A. Arrington, Robert West, Josef Michl J. Am. Chem. Soc., 1983, 105 (19), pp 6176–6177 doi:10.1021/ja00357a048
9. ^ Infrared spectroscopic evidence for silicon-oxygen double bonds: silanone and the silanoic and silicic acid molecules Robert Withnall, Lester Andrews J. Am. Chem. Soc., 1985, 107 (8), pp 2567–2568 doi:10.1021/ja00294a070
10. ^ Example Ar*tBuSi=PAr* with Ar* 2,4,6-trisiopropylphenyl and tBu tert-butyl in Ungewohnliche Reaktivitat der Silicium-Phosphor-Doppelbindung in einem Silyliden(fluorsilyl)phosphan: intramolekulare C,H-Inserierung und seine Umwandlung in ein neues Silyliden(silyl)phosphan M. Driess, S. Rell und K. Merz Z. Anorg. Allg. Chem. 1999, 625, 1119±1123
11. ^ The First Genuine Silicon-Sulfur Double-Bond Compound: Synthesis and Crystal Structure of a Kinetically Stabilized Silanethione Hiroyuki Suzuki, Norihiro Tokitoh, Shigeru Nagase, Renji Okazaki J. Am. Chem. Soc., 1994, 116 (25), pp 11578–11579 doi:10.1021/ja00104a052

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