Double bond rule

The double bond rule states that chemical elements with a principal quantum number greater than 2 for their valence electrons (period 3 elements and lower) tend not to form multiple bonds (e.g. double bonds and triple bonds) with themselves or with other elements.[1] The double bonds, when they exist, are often weak due to poor orbital overlap. Although such compounds are not intrinsically unstable, they instead tend to polymerize. An example is the rapid polymerization that occurs upon condensation of disulfur, the heavy analogue of O2. Numerous violations to the rule exist.[2]

Double bonds for carbon and nearest neighbours
B
boron
(n=2)		C
carbon
(n=2)		N
nitrogen
(n=2)		O
oxygen
(n=2)		Si
silicon
(n=3)		P
phosphorus
(n=3)		S
sulfur
(n=3)
B diborenesalkylideneboranesaminoboranylidenes, rare[3]oxoboranes, rare,
rapid oligomerization[4]		borasilenes (rare)[5]boranylidenephosphanes, rare, stable compounds are known[6]thioxoboranes, rare[7]
C alkenesiminescarbonyls, oxonium ionssilenesphosphaalkenesthioketones
N azo compoundsnitroso compoundssilanimines, rare, easy oligomerization, observed only at low temp[8]phosphazene (P=N)sulfilimines
O dioxygensilanones, Si=O bonds extremely reactive, oligomerization to siloxanesnumerous, e.g. phosphine oxides, phosphonates, phosphinates,
phosphates		sulfinyls
Si disilenessilylidenephosphanes a.k.a. phosphasilenes, rare [9]silanethiones, rare, easy oligomerization[10]
P diphosphenescommon, for example in thiophosphates and in phosphine sulfides, for example triphenylphosphine sulfide, certain dithiadiphosphetanes
S disulfur, thiosulfoxides

Other meanings

Another unrelated double bond rule exists that relates to the enhanced reactivity of sigma bonds attached to an atom adjacent to a double bond. In bromoalkenes, the C–Br bond is very stable, but in an allyl bromide, this bond is very reactive. Likewise, bromobenzenes are generally inert, whereas benzylic bromides are reactive. The first to observe the phenomenon was Conrad Laar in 1885. The name for the rule was coined by Otto Schmidt (1874–1943) in 1932.[11][12]

References
  1. Jutzi, Peter (1975). "New Element‐Carbon (p‐p)π Bonds". Angewandte Chemie International Edition in English. 14 (4): 232–245. doi:10.1002/anie.197502321.
  2. West, Robert (2002). "Multiple bonds to silicon: 20 years later". Polyhedron. 21 (5–6): 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 Rosas-Garcia, Victor M.; Crawford, T. Daniel (2003). "The aminoboranylidene–iminoborane isomerization". The Journal of Chemical Physics. 119 (20): 10647–10652. Bibcode:2003JChPh.11910647R. doi:10.1063/1.1620498.
  4. Vidovic, Dragoslav; Moore, Jennifer A.; Jones, Jamie N.; Cowley, Alan H. (2005). "Synthesis and Characterization of a Coordinated Oxoborane: Lewis Acid Stabilization of a Boron−Oxygen Double Bond". Journal of the American Chemical Society. 127 (13): 4566–4567. doi:10.1021/ja0507564. PMID 15796509.
  5. Franz, Daniel; Szilvási, Tibor; Pöthig, Alexander; Inoue, Shigeyoshi (2019). "Isolation of an N‐Heterocyclic Carbene Complex of a Borasilene". Chemistry – A European Journal. 25 (47): 11036–11041. doi:10.1002/chem.201902877. PMID 31241215.
  6. For instance Ar*P=B(TMP)2 with TMP = 2,2,6,6-Tetramethylpiperidine and Ar* = 2,6-dimesityl-phenyl Rivard, Eric; Merrill, W. Alexander; Fettinger, James C.; Wolf, Robert; Spikes, Geoffrey H.; Power, Philip P. (2007). "Boron−Pnictogen Multiple Bonds: Donor-Stabilized PB and AsB Bonds and a Hindered Iminoborane with a B−N Triple Bond". Inorganic Chemistry. 46 (8): 2971–2978. doi:10.1021/ic062076n. PMID 17338516.
  7. Tokitoh, Norihiro; Ito, Mitsuhiro; Okazaki, Renji (1996). "Formation and reactions of a thioxoborane, a novel boron-sulfur double-bond compound". Tetrahedron Letters. 37 (29): 5145–5148. doi:10.1016/0040-4039(96)01039-8.
  8. Zigler, Steven S.; West, Robert; Michl, Josef (1986). "Observation of a Silanimine in an Inert Matrix and in Solution at Low Temperature". Chemistry Letters. 15 (6): 1025–1028. doi:10.1246/cl.1986.1025.
  9. Example Ar*tBuSi=PAr* with Ar* 2,4,6-trisiopropylphenyl and tBu tert-butyl in Driess, M.; Rell, S.; Merz, K. (1999). "Ungewöhnliche Reaktivität der Silicium-Phosphor-Doppelbindung in einem Silyliden(fluorsilyl)phosphan: Intramolekulare C,H-Inserierung und seine Umwandlung in ein neues Silyliden(silyl)phosphan". Zeitschrift für Anorganische und Allgemeine Chemie. 625 (7): 1119–1123. doi:10.1002/(SICI)1521-3749(199907)625:7<1119::AID-ZAAC1119>3.0.CO;2-1.
  10. Suzuki, Hiroyuki; Tokitoh, Norihiro; Nagase, Shigeru; Okazaki, Renji (1994). "The First Genuine Silicon-Sulfur Double-Bond Compound: Synthesis and Crystal Structure of a Kinetically Stabilized Silanethione". Journal of the American Chemical Society. 116 (25): 11578–11579. doi:10.1021/ja00104a052.
  11. Schmidt, Otto (1932). "Über den Ort der Sprengung von C—C-Bindungen in Kettenmolekülen". Zeitschrift für Physikalische Chemie. 159A. doi:10.1515/zpch-1932-15931. S2CID 99620074.
  12. Hoogenboom, Bernard E. (1998). "A History of the Double-Bond Rule". Journal of Chemical Education. 75 (5): 596. Bibcode:1998JChEd..75..596H. doi:10.1021/ed075p596.
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