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The +M effect, also known as the positive mesomeric effect, occurs when the substituent is an electron donating group. The group must have one of two things: a lone pair of electrons, or a negative charge. In the +M effect, the pi electrons are transferred from the group towards the conjugate system, increasing the density of the system.
Prior to Typhoon Yagi forming and making landfall in Vietnam, domestic media reported unusual weather patterns in August 2024. Speaking to the Natural Resources and Environment newspaper, Mai Văn Khiêm, Director of the National Center for Hydro-Meteorological Forecasting, stated that the country's average temperature reached 28.3 °C (82.9 °F), the highest in recorded history. [1]
Contributing structures of the carbonate ion. In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or forms, [1] also variously known as resonance structures or canonical structures) into a resonance hybrid (or hybrid structure) in valence bond theory.
However, another effect that plays a role is the +M effect which adds electron density back into the benzene ring (thus having the opposite effect of the -I effect but by a different mechanism). This is called the mesomeric effect (hence +M) and the result for fluorine is that the +M effect approximately cancels out the -I effect.
This effect is depicted in scheme 3, where, in a para substituted arene 1a, one resonance structure 1b is a quinoid with positive charge on the X substituent, releasing electrons and thus destabilizing the Y substituent. This destabilizing effect is not possible when X has a meta orientation. Scheme 3. Hammett Inductive Mesomeric Effects
Vietnam's economy continues to expand at an annual rate in excess of 7%, one of the fastest-growing in the world, but it grew from an extremely low base, as it suffered the crippling effect of the Vietnam War from the 1950s to the 1970s, the punitive embargoes of the United States and its allies, as well as the austerity measures introduced in ...
On 4 July 1968 the base was subjected to a heavy People's Army of Vietnam (PAVN) rocket and mortar attack followed by probes on the base perimeter resulting in 5 U.S. and 16 PAVN killed. On 23 February 1969 the base was attacked by PAVN sappers.
The situation in South Vietnam continued to deteriorate with corruption rife throughout the Diem government and the ARVN unable to effectively combat the Viet Cong. In 1961, the newly elected Kennedy Administration promised more aid and additional money, weapons, and supplies were sent with little effect. Some policy-makers in Washington began ...